PSA : Don't Ban New Champions Day 1
You need to learn how to play with/against/as the new champion, so don't go banning them out on day 1 because you're scared of change.
Kayn is not broken, he's different. His early game is weak and gets weaker until he transforms. Learn how he fights and how he builds, then after a week go ahead and ban him if you still think he's worth the wasted ban.
People are excited for him because he's fun not broken, and will be a popular champion because of it. People are only comparing him to Yasuo because he has a dash that spins, that's it, that's as far as that kit comparison goes.