Here's a copy of his comment:
Hey all, lots of great points brought up in this thread. With legendaries the amount of unique anims and how drastically they change can vary from Champion to Champion. With newer Champions they can sometimes have massive animation suites, so rather then give them 100% unique anims we just tweak the base ones. This was a approach we took for both Nightbringer Yasuo and and Dark Star Thresh since they were much newer Champions. New Kayle has a enormous animation suite, between 4 forms, enraged/non-enraged AAs, Melee/ranged AAs, High Attack Speed/Low Attack speed AA, so we had to chose carefully where to put the unique animations for Kayle. We ultimately chose to put the unique anims into her mechanical wings, which do have a new animation suite compared to base Kayle as we felt her mechanical wings are the most unique aspect of the skin. The Death anim is a good call out though and we will be adding a unique death anim to her soon, targeting next patch. We will also be adjusting AWs Auto attack SFX to match closer to old AW SFX.