And with stuff like Yasuos wall they have always stuck to the thematical is it a projectile really? kind of thing.
They didn't use thematics to answer that question. They made a strict definition. A projectile is something that has a start point, an end point, and a travel time in going between those. Lux's ult does not have a travel time, so it's not a projectile. Thematics didn't come into it. Rules did.
he only thematic consideration I can think of is how Ziggs ult goes over the windwall, and that's primarily because it would supremely confusing if a projectile that wasn't even on the screen disappeared because of something that wouldn't appear to visually be anywhere near the projectile and that the Ziggs player couldn't necessarily even see.
Yeah I was just wondering though because it doesn't really make sense thematically
It does make sense from gameplay terms though. Damage and CC knocks Taliyah off of the wall. Traps are CC, so they knock her off of the wall.
Exceptions to the rules are something we should avoid unless we have no other choices. The last thing we want is for people to have to memorize a list of exceptions when trying to learn the rules that determine what abilities do.