High skillcap champs like Yasuo or Thresh or Lee are on a neverending winding path to destruction

The title might be a bit overdramatic but the point still stands. Champions with extremely loaded kits that are difficult to use as a base but with crazy plays possible (bunnyfufu thresh) will almost always be hated since you feel helpless if they play their kit well since any other champion's potential isn't as high. Because of this, after the initial nerfing to create a skill floor, the champion is on a neverending path to destruction because of previous bias against the champion and the fact that Riot refuses to nerf anything about them other than their raw power. This is probably the reason why Riot is very judicious when nerfing things like Lee/Yasuo/Thresh. It's because if they keep on cutting numbers, there's gonna come a point when they are abysmal in the hands of the average and average to good in the hands of the master. Lee Sin has already seen his share of the initial pruning to create a meaningful skillfloor; he has lost a lot of his raw dueling power in his W/E and although his Q/R are very powerful, he is actually rather bad as a duelist when compared to other bruisers such as Xin/Irelia/Rumble. Any further pruning to satisfy the bloodthirsty crowd will continue to put him upon this winding path and the moment he stops seeing LCS play, he will likely be Urgot tier or just a few notches above Urgot in terms of strength.

I realize that some people might bring up Shaco as an example, but Shaco's kit actually has a lot of raw, albeit difficult to use power in it through the clone and W and his kit/role doesn't lend itself to the LCS as easily as Lee or Thresh or Yasuo might so the comparison isn't exactly fair.

tl;dr it is impossible to meaningfully nerf a high skillcap champion because they will either very steeply scale with your skill as a player so that the majority isn't good at them at all or they will be the worst of the worst where nobody can make them work.