90% of the problems caused by assassins are from their animations

And by animations, I mean animation cancelling. That's 90% of what makes assassins broken because of how much extra damage they can stuff into an extra tiny timeframe.

That's why a good LeBlanc will nuke you with next to no mercy or fair time to react.

Or Talon/Rengar with their 100-0 combos in less than half a second.

And then you have Yasuo and Riven who are the poster children for how animation cancelling triples a champions skillcap by quadrupling their damage output. No really, Yasuo can wall mid-Q, Q mid-E (to be fair this one is intentional), wall mid-E, and wall mid-ult. Yasuo should be vulnerable during his ultimate but because of how he can cancel animations he's a lot more oppressive and safe than he should be.

I can guarantee you if something is done to restrict the amount of actions that can be completed during a leap, while projectiles are in the air, or while you're completing a self CC movement, assassins can be buffed to be playable without being good solely due to a hilariously frustrating mechanic.