My thoughts on Kayn.
Personally I really like Kayn. In fact I would even go as far as to say that he's my new favorite champion. I know he hasn't been out for long, but for some reason this champion just clicks for me. Like, seriously, I haven't had this much fun playing league since old Rengar was a thing! Now I understand that Kayn's winrate isn't very high right now, but now that he's been buffed he's actually genuinely good regardless of which form you go into. I've noticed that most people prefer Rhaast over Shadow Assassin Kayn, and while I do really like Rhaast I personally prefer the Shadow Assassin form. I will admit thought that I'm biased since assassins are my favorite class of champion.
Now then, most people would agree that Kayn is a little bit on the weak side, and while he could be stronger, he's certainly not weak. If anything he's actually pretty good. The only reason why people think he's weak right now is because most people have mistaken him for being an early game jungler, which couldn't be farther from the truth. Sure, he has really high mobility, decent sustain and clearing speed, and some of the best base stats while also having some of the worst growth stats, but he's actually very weak early on. He doesn't truly become a force to be reckoned with until he transforms. Speaking of which, I really like how players have the freedom to choose which form to go into, but it kinda sucks how sometimes players have to wait four minutes to go into the form they REALLY want to go into. If anything, players ought to have the freedom to instantly choose which form they want to go into. (That's just my opinion tho plz don't sue me plz and tank you).
And one more thing that's kinda random. When playing Shadow Assassin Kayn, I've noticed that when using his E, you can still hear Rhaast even though he's supposed to be dead. Soooo yeah, might wanna adjust that audio Rito lmao.