Being blinded, grounded, silenced, or debuffed (movement slows, attack speed slows, sight reduction, etc.) won't count. Just about all other cc counts as immobilizing a champion, with polymorph and stasis being iffy cases that may or may not count.

learn a new champ nerd

https://lolalytics.com/ranked/world [...] champions/
I often do statistical analyses of League items/champions/runes etc. on my own time, usually to know before most what's sleeper overpowered (incredibly successful but uncommon), such as unusual builds/rune setups or underrated champions.
I've looked at the performance of some of the more controversial keystones and attached my impressions below. Let me know if there is anything you'd like me to add.
 
Summon Aery
 
What you'll notice first is that even every poke-oriented champion tends to win a fair bit more with Summon Aery than with Arcane Comet, e.g. Xerath, Ziggs, Zilean etc. are slightly more successful with Aery than Comet. This is clearly stupid, because then Aery's intended users (Sona, Nami, etc.) don't even come anywhere close with any other runes as they do with Aery.
So clearly Aery is overtuned offensively. It could use some identity-sharpening. (Is it really a hybrid rune or just extra poke damage?)
 
Arcane Comet
 
Mediocre. It does fine on a fair bit of mages (49-42% range) but often underperforms compared to Aery.
The main issue with Comet is its utter lack of identity. It seems to be a poke-oriented rune in that it's a long-range extra damage proc on a moderate cooldown.
But it also seems to be a crowd-control, burst-combo mage rune, because its damage is dependent on landing, which is only guaranteed when landing a CC ability (I.E. Xerath's Stun, Lux's Binding, Syndra's Stun, Brand's Stun, etc.) but then the rune is just extra damage on a combo, which makes it fill Electrocute's niche.
But even then, they added a cooldown reduction to the rune for users who repeatedly damage enemies, which orients Arcane Comet towards champions who spam/deal DoT so they can proc it as frequently as possible.
It's apparent that Riot tried to make one keystone rune be a mediocre solution for every single mage in the game, and succeeded. No mages are succeeding nearly as often with Electrocute, with Phase Rush, etc. And they all have 'alright' performances with comet. How utterly boring for the midlane. God willing, Riot might give mages Stormraider's Surge back sometime before Preseason ends.
 
Speaking of Stormraider's Surge:
 
Phase Rush
 
Decent on bruisers, worse than Resolve keystones on tanks.
Absolutely fucking awful on the majority of its previous users. (All mages.)
Where you'll find winrates in the 49-54% range, varying by champion, when looking at mages' performance with Arcane Comet and Summon Aery, you'll pretty much invariably find that Phase Rush has a ~42% winrate or so, so bad that it's similar to not taking a keystone at all on the old system for many mages.
I'm especially perplexed about this rune because when Riot polled which rune the playerbase most wanted to return, the response was overwhelmingly Stormraider's Surge - but then they took the Surge replacement away from all of the people who were requesting it...and gave it to melee bruisers/assassins.
It's still decent on some, such as Yorick, and Kha'Zix, but the closest it ever comes to being decent on a mage is its gross ~46.5% winrate on toplane Karthus. Comparitively, it has a 42.8% winrate for him midlane.
Keep in mind that Riot repeatedly insisted that we just weren't realizing how good it was on these mages. Apparently, taking a group of mages' rune, gutting its speed value, increasing its cooldown, taking away its slow resistance for non-melees, and then making it drastically more difficult to proc leads to a rune being much worse.
Who could have known, except for anyone capable of common sense or basic logical reasoning?
Okay, so Riot blundered massively with the Sorcery Keystones. But let's move on to something more interesting.
 
The keystone you've all been waiting for:
 
Kleptomancy
 
Strap in, because we're going deep.
In terms of actual performance/power, Kleptomancy is...
. . .
Highly overrated. I want to emphasize a particular point here, which is apparent versus actual power.
Ardent Censer and Janna both had obscene levels of power, but, much like the old MR-Aura Aegis, had their power well-hidden. It's much more subtle than the in-your-face orbital beam of Redemption, for example. So they flew under the radar. Conversely, champions which are horrendous to play against are often left very weak because of how powerful they feel when playing against them. An example could be how Leblanc will be considered stronger than Sona (because Leblanc feels like bullshit to face, and Sona's power is much more subtle) even if LB has a 48% w/r and Sona has a 54% winrate.
To the point: Kleptomancy is more like Leblanc; it feels much more powerful than it actually is.
Kleptomancy is INCREDIBLY SATISFYING, very fun to use, and very viscerally rewarding. So its users tend to freak out and think it's broken - even when it isn't actually too successful compared to many other keystone runes.
Keep in mind that Kleptomancy isn't pure RNG. It's pseudo-RNG, heavily tuned to give an approximate range of gold and certain items at certain moments in the game. So it isn't as wildly variant as you might think.
Last note: Klepto is ridiculous on a couple of champions. Sona - who's grossly overpowered anyway - and Ezreal in the ADC role, having spiked them to the top of the charts in each of their respective roles.
THAT SAID, Kleptomancy is NOT OVERPERFORMING ON GANGPLANK. It has approximately a 49.4% winrate. Would you believe that even Grasp of the Undying and Summon Aery out-perform Kleptomancy on him?
Yes, it's fun. Yes, it feels powerful. But it's very well balanced (and very well designed.) The only champion who is overpowered with the rune strictly because of the rune is Ezreal, and, given that now his JG relies entirely on his Q applying red buff, and his ADC relies entirely on his Q applying Kleptomancy, it may be that a change to Ezreal himself is in order - not the rune.
Now, something bad.
 
Glacial Augment
 
Is Glacial augment decent?
In some niche cases, like Zilean mid, and on some supports.
The issue is that every glacial user has a better keystone elsewhere. GLP users aren't going to take it usually because a damage keystone will do them better. Auto-attacking supports who aren't tanky are more likely to take Kleptomancy. Melees who want to chase a target down to kill them might as well take a Precision or Domination rune so they can actually kill the target to begin with. Tanks who could apply it in an AoE on Randuins aren't going to give up the broken Resolve keystones for this.
And then there's Gnar, for whom Glacial Augment is pretty bad. 46.76% winrate.
Other chasing champions don't fare much better. Tryndamere rocks an impressive 42.35% winrate with this keystone.
Then it seems decent on some rare cases, like Teemo, who has a 51.37% winrate -- but then you realize that Teemo has a 54% winrate overall, and is much better (3-4% higher winrate) with virtually every single keystone except Lethal Tempo.
My guess: Riot undertuned Glacial Augment out of fear of creating a perma-kiting situation, like Frozen Mallet in a keystone, for ranged toplaners. They also split the keystone's effectiveness between auto attacks and active items, but most champions are only one or the other. (An active slow item user or a regular auto-attacker.) This rune could use some work.
 
Next, the sleeper keystone:
 
Grasp of the Undying
 
Seems to be plainly overtuned.
This becomes apparent when you take a quick look at Yorick's performance with the new Keystones.
He was initially thought to be OP this patch, but what you'll notice is that his newfound high winrate _only appears when using the new Grasp of the Undying, landing him at . The only other comparable rune for him is Phase Rush, which performs well, but is also nearly 1/40th as popular (which typically means it's being used in niche cases by one tricks/mains/rune-specific counterpicks, artificially inflating its winrate.) This reminded me of how tanks seem to have become supreme in toplane again, due to suddenly and inexplicably becoming immortal by mid-game. You may know this already if you've had the misfortune of playing versus a Maokai at all this patch.
Anyway, it's unclear whether Grasp itself is overpowered or the Resolve Runes in general are overpowered, inflating Grasp's winrate, since runes like Aftershock have a similar performance on Maokai (both giving him an almost identical 53.7% winrate.)
It could be, of course, that all of the Resolve runes/keystones are just overtuned. Likely because, as I mentioned with Kleptomancy, subtle power often goes unchecked. It's much easier to feel the damage of Scorch than it is to appreciate the survivability of one of the 5 armor/MR runes, even if those ones are actually stronger.
 
So keep an eye on who can abuse these Resolve runes. In some cases, such as Riven, Aftershock performs even better than offensive keystones. Which leads us to our next analysis:
 
THE DOMINATION KEYSTONES (Electrocute, Predator, and Dark Harvest)
 
Suffice it to say that none of these runes appear to be overpowered, and in some cases, appear to be bad.
First, a look at Dark Harvest. Take a look back at my Kleptomancy analysis of actual vs. perceived power and consider how many HOLY F#$KIN MOLY DARK HARVEST QUADRUPLE ONE-SHOT videos we had leading up to Runes Reforged's release.
It's very possible that the rune having its power concentrated into a sudden, initial, often unexpected burst made the rune appear more powerful than it actually was, especially in conjunction with the PBE hype (where it was much easier to snowball and stack the rune to unrealistic levels due to the imbalanced PBE matchmaking.)
Now, that isn't all to say that Dark Harvest is bad. It performs just fine on Kha'Zix, about equally as well as Electrocute and Phase Rush on him, but then falls flat on, for example, Kayn - though this is likely because its effectiveness drops sharply when he's going Rhaast but already took Dark Harvest due to anticipating a Shadow Assassin game.
 
Electrocute is just about Average.
To give you an idea, it performs slightly-sub-50% on Riven, slightly-above-50% on similar champions like Jayce, and then just about 50% on Kha'Zix.
What you'll notice, however, is that, unlike Thunderlord's Decree, Electrocute seems wildly variant on mages.
Zilean, who was previously a core TLD user, wins only just under 47% of the time with Electrocute, even though it's much easier to proc on him now, as his E-slow and a bomb attaching both stack the rune now. (But he's not crying because he has plenty of other great options.)
Syndra is just awful this patch, rocking a staggering ~45% winrate. That said, Electrocute seems fine on her, just worse than Aery, which, as we know, is overpowered.
Most mages, however - Lux, Brand, Zyra etc. either have underwhelming (~48% range) success rates with Electrocute or are just clearly worse with Electrocute than with other options.
 
One more thing:
**Predator seems to be awful on a lot of champions, if you just go by winrates.
But often times, active items have their performance artificially deflated due to the increased skillcap associated with them. It's very likely that Predator is just fine, or very good, on many champions but its users are accidentally cancelling the channel, trying to figure out how to use it optimally, etc. so don't count it out quite yet.
Malzahar, for example, does just fine with Predator.
 
Alright, I'm getting tired, so I'll do one more analysis for now:
THE PRECISION KEYSTONES (Lethal Tempo, Press the Attack, Fleet Footwork)
 
This is likely the most well-balanced tree.
One observation that stood out to me is that Press the Attack is almost unanimously better than Lethal Tempo on every champion, though this is not always the case.
Have a look at Kog'Maw. What you'll find, shockingly, is that all of the keystones perform about equally on him - just about in the 50-51% winrate range. Twitch, by contrast, has a gross (54%) winrate with Press the attack, while being balanced with the other two keystones.
Our main man Jhin does just awfully with both Press the Attack and Lethal Tempo (unsurprisingly), slightly less awfully with Fleet Footwork, and actually performs fairly well with Arcane Comet!
Of course, Aery is still Jhin's best keystone, but as we've discussed, Aery is currently overpowered and will almost certainly have its offensive power tuned down.
Our main girl Jinx has a meh winrate with Lethal Tempo (slightly sub-49%), a fair 50% with Fleet Footwork, and a nice 51% with press the attack. I definitely didn't expect Press the Attack to outperform Lethal Tempo on auto-attack centric hypercarries like her, but here we are.
 
Closing
 
Alright, if there's anything else you'd like me to look at, let me know.
Off Meta Zilean