The only change master yi needs is to make his meditate uncancellable and unbreakable

That is, make meditate last for the full 4 seconds and don't give master yi the ability to cancel it, but don't give the enemy the ability to cancel it with cc either. That way, when you are able to force master yi's meditate, if you are dangerously low on hp you can just make a bunch of distance in 4 seconds and he won't be able to finish you off. If he is completely alone and you ambushed him to force his meditate, you can just wait it out and kill him. If he used meditate and his team is there to back him up, it is basically a big de-aggro, allowing his team to set up a defensive perimeter around him for when he comes out of meditate.

It has a 35 second cooldown and his ult only refreshes 70% on kill or assist, which still leaves 10 seconds. In other words, he will probably get off 2 maybe 3 meditates in a 5v5 max if he has 100% kill participation, and probably just 1 in a skirmish.

If you don't allow master yi to have this kind of de-aggro then the only way he can have a decent winrate is if he does so much damage so quickly there isn't really a lot of counterplay, if he resets his abilities completely on kill or assist, or if he's slightly tanky. We've already gone through each of those iterations of master yi, and they didn't work. His kit needs to work together to help him achieve his goals, and meditate isn't really doing its job because most high tier master yi players just use it as an auto attack reset mid and late game, and only use it defensively like once or twice in the early game.