i don`t understand why they nerf 
W damage reduction 60 >40 and nerf cdr
w for up to 4 seconds, healing himself every 0.5 seconds, increased by 0% − 100% (based on missing health). and damage reduction based on level 60 / 62.5 / 65 / 67.5 / 70%
dose`t damage reduction 60-70%
Yi is only as strong as your jungler allows him to be. His early game sucks and if your jungler gets your laners ahead or just straight up murders yi in his own jungle, he becomes useless.
Can Yi be frustrating? Yeah, when he's not delt with properly, but overall he's kinda bad the higher elo you get.
I'd say one thing that definitely made Yi more annoying to play against lately though is 
...guy is literally always in alpha
Because Yi has a bad early and doesn't have mobility like Irelia and he isn't a Tiamet user so he doesn't do Aoe
Cause Irelia has CC and already decent amount of tankyness. Yi is just a melee ADC, he needs means to survive like Yasuo and Fiora.
