Tenacity tends not to matter these days because even if you can reduce your time disabled down to 2 seconds, you'll be dead in 1.5 seconds. Not useful.
It feels to me like Tenacity just needs to be reworked. But how should it be done?
L Psy Kongroo2 votesTenacity is fine the way it is. The game just needs less cc. Not every ability needs to slow, not every new champion needs a stun or a knockup. CC in my opinion should be sparsely distributed but strong, and only certain classes (read: tanks, divers, and a few specific mages) should have access to it.
darkdill2 votesRiot won't allow the reduction of sources of CC because that'd break the game.
Kurt Hyzan1 votesNot really a good, things like 
would just be unstoppable if they focus on the main cc while ignoring getting cc'd
Tenacity should work the other way around as you stated imo, each next cc is reduced by a certain %
darkdill1 votesActually, that would work better.
CloudedLogic1 votesPersonally I think they need to re-rule which CC is affected by tenacity, as there is a lot of champs who simply have CC you can't reduce (I believe Blitzcrank's silence is the only thing in his kit affected by tenacity for example for the instant it even lasts). I would like to see more instances of the brittle status effect (though perhaps renamed to not be so champion theme unique), however perhaps it is because of my low rank but I pretty much never see anyone exploit the CC duration increase of brittle. Ornn literally always procs his knock back thing when I am playing.
Mordepool1 votesPerhaps it should charge up a Spell shield the charge time is based on % Tenacity
And slow immunity once you reach a certain threshold of Tenacity.
Reasoning:
Spell shields mitigate Displacements
The champions who stack Tenacity get fucked over by Slows more than any other class. Reward for investing in to it significantly
GodlyBane1 votesknock ups immunity
Teridax681 votesTo the first question: yes, Tenacity needs to change in at least some manner. It's a stat that has become increasingly lacking in clarity, on top of being increasingly weak in an environment full of CC that ignores the stat, and therefore its core purpose, entirely. Tenacity was a stat created to give certain champions a measure of resilience against some crowd control, but over time some Rioters decided their champion was so special that they deserved to ignore this completely, or at least that Tenacity itself was unhealthy enough to not need to counter their CC. Because of this, we're now stuck at a crossroads: do we want a world in which Tenacity properly reduces crowd control, or has the mechanic become obsolete? I think there are a few options that can be taken at this point:
#Option 1: Tenacity now reduces all CC, no exceptions This would be the most basic and direct solution. On the plus side, Tenacity would finally be consistent, and would therefore be a much more adequate response to teams loaded with crowd control. However, there are some risks here, because this would make some CC types less consistent relative to Tenacity in exchange. Already, champions who heavily rely on reducible CC, such as Fiddlesticks, Morgana and Rammus, have had major balancing issues in the past, because their CC needs to be inflated to deal with Tenacity users, but it also needs to be kept in control, otherwise it locks down people without the stat for far too long. As such, this might require a rebalancing of a lot of CC, and even then may make balance more brittle on certain champions.
#Option 2: Remove Tenacity, rebalance all CC This is the flipside, and a solution I'd personally prefer a little more. Part of the problem with Tenacity is that its existence creates the expectation that a champion needs to build the anti-CC stat in order to deal with certain CC types, and that tends to be a pretty band-aidy solution that doesn't really make for flexible gameplay (you lose harder than you should to the mechanic until you start countering it too hard). Removing this expectation, and rebalancing all crowd control to be more manageable at all times, could therefore make CC feel fairer as a baseline. The one issue with this is that it doesn't solve on its own the problem of some champion needing CC resistance more than others: juggernauts especially are far too vulnerable to CC, and would remain so after this kind of change, on top of feeling like they have even fewer options. Because of this, it may be necessary to do a pass on champions to give them innate CC resistance where needed.
#Option 3: More Quicksilver items/unstoppability A heavily underexplored mechanic in League is the ability to cleanse oneself of crowd control, or become immune to it. A few champions have it, but Riot's been super-cautious overall, even removing unstoppability from Ornn's W as a balancing measure. Enabling the option for more champions, especially those more durable and less mobile, to itemize for active CC resistance, rather than some passive stat, could be one way of letting them resist CC at crucial times, and so in a more skill-expressive manner. For example:
##Mercurial Mail:
+ 
+ 700g = 3000gNumbers are obviously not balanced, but that could be the general idea of a QSS item for tanks and fighters.
darkdill1 votesI'd change the passive effect to "Taking damage from enemy Champions causes Quicksilver's cooldown to cycle 100% faster for 1 second". This way, there's no difference between taking a bunch of tiny hits in a single second or just one hit. It's how HotS does stuff like that.
Teridax681 votesThat might work better, yeah. Ideally, this kind of cooldown should probably tick a lot faster in heated teamfights than in duels, but it shouldn't just abuse getting hit by quick basic attacks or DoTs.