Tenacity is an Invalid excuse. CC in URF needs individual addressing.
CC in URF is one of the most obnoxious things to deal with because of how low champion CD is in this mode. Problem is, Riot's "Solution" is to increase all champion Tenacity against CC.
And it does NOT work. Here is why:
By this Definition Tenacity reduces all forms of CC except Surpression, Stasis and Displacements. Incase people don't know, Surpression CC include
s Polymorph or Tahm's Devour and Displacement is basically EVERY SINGLE KNOWN FORM OF FORCED MOVEMENT
Just to make a list, these are all champions with ANY form of Displacement CC:

(Rhaast Form)

56 champions out of 146 have CC abilities (At least one, some have several) that are NOT REDUCED AT ALL by Tenacity, and while some have very minor durations, most of them are extensive, lasting up to 2 seconds in some cases.
Additionally, there are also Surpressions to account for, which include:

this is a total of 63 champions who have unreduceable CC. And the Forced Movement part from Displacements can't even be cleansed, meaning if you're Knocked up, knocked down, knocked aside or otherwise displaced by an enemy Ability, such as Lee Sin R, you can use cleanse against his Ult, but you will STILL fly the full duration so cleansing was not only useless but now you have a cleanse on CD, and if it was the Summoner Cleanse or QSS, you will have to draw fights out to not die again until CD is back up.
THEN you have Champions who pack such long CC durations, combination of CC in several abilities OR such short Cooldowns that even with Tenacity, it's absolutely useless because the CC duration is longer than the Ability Cooldown and you get permanently chained.
Such Abilities come from these Champions:

So now we have a total of 75 champions who's CC is impossible to deal with, no matter what you do, once you are caught in it.
THEN there is also Stasis CC, which is equally unaffected by Tenacity as are displacements, and Champions with Stasis against other champions are:

Note that the total number of Champions currently is 146. 73 would be 50% of the champions. Our Number of Undealwithable CC is 77, meaning that that is just 4 champions over HALF THE ENTIRE CHAMPION POOL.
You can't deal with literally over 50% of the entire Champion pool because the CC they press out is a permanent prison and thus your death sentence the moment you are caught in it.
Saying "We give everyone increased tenacity to deal with it" is an absolutely useless would-be defacto solution which serves ONLY as a pseudo-valid excuse to refuse having to actually address all the problematic Abilities, I mean hell, half the entire champion Pool needs individual addressing and CC duration reductions. So many games are decided by who has more CC rather than who has better damage that it's become a complete gamble. The moment you enter loading screen and see enemy champs with more CC than your team, you know you lose this game unless they have an AFK or at least one person is entirely new to the champ they play.
I thought URF was repeatedly balanced and fixed with the intention of it NOT being a game mode decided from the very start. Riot Literally made champion selection All Random so one side no longer takes the OP picks and auto-wins. Healing and Shielding reductions were equally introduced to make self-sustain Champions not as broken as they could be. Every Restriction in URF was aimed specifically to make champions fair and balanced in a 5v5 scenario. So why is CC not included? Or at least, why only partially?
Why are so many CC Abilities in URF still allowed to be borderline unfair?