The Issue with Kayn.
Its no debate, with his abysmal win rate, he is clearly a bad champ. However, neither his blue or red form, are bad by any means.
The issue lies in his base form. His base form is the WORST champ in the game, because of this his ganks are bad, his lane phase is bad (if youre laning), and it becomes a struggle just to become a viable champion(working towards Red/Blue). A struggle that all too often leads to Kayn unavoidably going like, 0-5 before he has a chance to be a real champ. If he doesn't get lucky early game kills, and they are indeed lucky kills considering how weak he is early. Pure luck. If he doesn't get those luck kills, he is completely terrible for the whole game.
In my opinion his base form should be significantly buffed. At lvl 6 and every rank of his ult, you should be able to select a form.
The difference in base form to Blue/Red shouldn't be so much in the numbers, but more in slight playstyle shifts....