Whatever you do to balance out Kayle, Riot, don't buff her early game
Kayle should get stomped on by just about everyone in early game because once she hits late-game, she's like the Goths in Age of Empires 2. Once she's gotten to level 16, it's no longer a case of the enemy team asking "What can I do to stop this from going bad?" because it's already gone bad for them.
So even if Kayle gets a low winrate, don't buff her early game. That should be a permanently intended weakness.
, AOE true damage on auto-attacks, resist-shredding, a %-missing health attack, and the ability to negate burst damage? That is simply broken.