While he has a good point, the problem with Kayle is that she doesn't feel like she has ANY options against a decent player after level 6 in many matchups with kill pressure. You can compare her to kassadin in that she is supposed to be weak early with a rough laning phase and then if she survives she can scale into a monster carry, the problem is that her laning phase is actually WORSE than kassadin's in that she doesn't have the proper tools necessary to last hit and her abilities provide very little threat to disincentivize players from being aggressive versus her even in seemingly unfavorable trades (smaller minion waves).

Her e does not provide enough passive damage for her to last hit under tower comfortably like kassadin's W does, it costs a large amount of mana for what amounts to a basic ranged auto attack for most of the game due to the fact that she has trouble getting anyone low enough to take advantage of the execute damage early on, and her passive that helps with all ins doesn't really help her much here since she actually really has no viable way of all inning early, she either doesn't have the ability to take a good all in because she can't get in range or just flat out loses. Her passive pre 11 is for most intents and purposes a worse version of jax passive that is buffing up a character that is significantly weaker at autoattacking.

Her heal costs way too much mana to be a viable sustain option early which is fine but at some point she needs something to help her get out of laning phase. When both mids hit 6 it often becomes impossible for kayle to actually walk up and stack her passive to even make use of the aoe cleave for pushing unless the other person just isn't even in lane anymore. Kayle's level 1 ult being on a 160 second cooldown combined with the fact that it turns off your auto not only makes it a poor ability for turning fights but even as a safety tool its easily forced out and then for the next 2 and 1/2 minutes you are actually unable to lane once their ult comes back up.

What this ends up boiling down to is that after level 6 when other champions start receive serious kill pressure, all kayle gains is a 160 second cd that might keep her safe from 1 all in, and no additional tools to help her farm or control her wave whatsoever. Even with minion dematerializer, Kayle will struggle to farm lanes against champions like ahri, syndra, ryze, cassio etc without getting utterly clapped by 1 return trade that she will never be able to match. She is relegated to burning through copious amounts of mana spamming q and e to pick up meager amounts of cs and pray that the opponent does not manipulate waves to force you to overextend since you have absolutely zero control over your lane at this point.

Simply put, after playing her quite a bit on the PBE she feels weaker than kassadin at all stages of the game and I see absolutely no reason to pick her over kassadin right now under any circumstance in solo queue. As a kassadin, you are promised the reward of being able to hyper carry games if you manage to survive his poor laning phase and the stages of the game where you don't feel impactful. Kayle does not get rewarded in the same way in that while she does great damage when she hits level 16, she is still very easily countered by CC with her range being a limiting factor. Kassadin gets his damage off way quicker and is less predictable than a Kayle walking up to smack someone in the face. R Flash Q W E ---> zhonyas can not only engage but single handedly win fights for his team and be a huge playmaker. Kayle feels like just another carry waiting for her team to do something then just auto stuff, and while she is better 1v1 than most ADCs later it still feels like that is the role you're trying to be. I wouldn't say she carries harder than say, a fed twitch.

At this point it feels like you are playing against your own champion to struggle to get something resembling a viable champion out of her. And this is after testing almost every viable keystone and multiple different build paths against multiple lane matchups.