Just fyi this isn't my main account. I've been trying to main Shen for a bit now but what frustrates me about him are the annoying matchups. Darius, Morde, Fiora, Neeko, Gnar, Garen, Vlad every game. Shen doesn't scale poorly but he doesn't scale well enough to make it ok to have a bad early game.
Kayle doesn't seem to have any terrible matchups. Tryndamere and Jax can be scary but they are both very winnable skill matchups. I also noticed that even if I int early game there's basically no consequences, klepto is a bs rune and once you hit level 11 you turn into a farming machine. Your e execute + cou de grace also makes it very easy to ks and scale even faster.
Basically what I'm saying, for a lategame champion she has a VERY strong early game. She completely crushes actual early game based champs like Garen Morde and Darius and just uses them to free farm klepto. If you ever fall behind you just farm like mad with your aoe and use your execute to ks shutdown kills.
I've spammed like 50 games of Kayle on my main and so far it seems like the only reason I ever lose is either botlane ints too hard (ironically why I started maining Shen) or our team comp just lacks frontline. I always outperform and outfarm my top lane opponent 100% of the time though. It seems like the Kayle re-rework has brought Kayle full circle to her early season 4 days as a lanebully hypercarry.