Faceroll. I despise that word because of how wrongly it´s used to define champions. Kayle is not a faceroll champion. Neither are Katarina or Yi. Each one has their own little mechanics that the player needs to master properly in order to do well. They are simple champions overall, but what makes them truly hard is all those little details.
A Kayle mid first timer can grab Exhaust against a Yasuo and still feed him.
A Kat needs to use their resets to their maximum in order to get more of them.
A Yi needs to know how to weave Qs to avoid CC and know how to use W.
A Kayle absolutely needs to know who to ult and when to ult. When and who to slow. When and who to heal. Who to aim her AAs at. And how to kite.
So no, Kayle is not faceroll at all and neither is her gameplan. She's not Riven levels of complicated, but far from faceroll.
The problem is not Kayle. She simply synergizes well with certain items that wouldn´t exist were it not due to her. I mean, Azir wouldn´t even build Nashor's if not for Kayle, and her high winrate is due to her low playrate.
Nearly no one plays her. And those who do, know her inside and out, as well as the matchups she does well against. I´m not one of those, but i´m slowly getting there.
If she was so much of a problem, she'd have Lucian levels of playrate and an enormous winrate, which she doesn´t, because she has matchups she struggles against and is actually well within the balanced side of things. Hence why, with the exception of release Devourer -5AD nerf, she hasn´t received one, and the only one planned was reverted because it would nearly gut her.