Overreaction on reversed moralities of twin sisters and that how their themes clash and contradict are just ignorant analyzes of what they were meant to be.
First. Let's star with Kayle. Our divine justicar, an angel knight archetype carrier shaped and made more unique in LoL universe. Kayle uses holy light to punish the evil. Hmm... Does it ever sound familiar? Angel. Holy. Punishment.
Church and their actions upon the "evil" were so bad that they arent even questionable unlike Kayle actually. Holy light with shinning gold armor combined with clean bird wings doesn't make someone SAINT.
Kayle is also a representation of how having benevolent thoughts dont make you perfect. She is dilueted church that still has her moral strengths. She is flawed obviously but she is trying her best. And since it is just beginning of her story, give her enough time to develop. Bios are emotionless and they are not written to tell everything.
Lastly for Kayle, If you were looking for her to be goodness incarnate, you are already wrong since the beginning. Because she wasn't either in her old lore. They stayed LOYAL to her personality, they just made it in an actual piece of lore unlike as the almost non-existing backstory.
(*Cant go without saying, keep in mind, non-existing backstory may opened doors for headcanons for so long that you might shaped a Kayle in your head that actually doesn't exist and accept it. A possibility you know.*)
Morgana though... She is a little bit tricky. I agree for now that she looks too benevolent she makes her sister worse than actually she is. But according to her writer she is bitter and merciless in certain moments. She has flaws, just bio wasn't obvious enough to give it to reader.
Also Morgana, or better I should say, the readers, suffer from sympathezing freedom seekers so easily. Morgana uses a theme that gives reasons for flaws, and with that reasons people ignore the flaws... Doesn't mean they are justified. Look at killing Ronas.
I think writers are doing magnificent job right now and before witchhunting the lore, I would wait content coming soon a bit more! We haven't even heard their VO's yet. Kayle could be more sympathetic, Morgana could be more sinister. While listening their trailer, Morgana did not sound like an actual angel to me you know. (Perspectiveee....)