Now, to start things off, please do hear me out.
I love, Kayle's pre-rework design, it's one of my favorite design's in the game and for me personally unmasked kayle is the closest thing I can have for a perfect Default Skin. So now you may be wondering then, why defend this change to Kayle and it's for quite a simple reason.
It's because from a designer's point of view, it makes perfect sense.
We actually have a tweet by Spideraxe that gives a bit more insight at this.
For new players, getting into a game against a champion you dont know, visuals may be your only aid to figuring out how a champion works and this works quite simple, most of us do it quite regularly with new champions too.
If they have a ranged weapon, they're most likely a carry,
Anyone with a spellbook or magic particles is probably going to itemize into AP
A lean looking character with a smaller weapon is most likely an assassin
And someone in a massive suit of armor is most likely a tank.
Kayle's current design, while fitting for her personality and lore, Clashes with her role in game and could potentially cause confusion. So the design was changed. And this isn't to say her new design is particularly good or bad, but at least it may give some insight on what Riot was thinking when they redesigned Kayle like this.
Though in my personal opinion they could have simply gone with a smaller armor set instead of removing most of it, such as in the popular redesign that has been floating around lately.
Though that is only my opinion.