Knockbacks on innitiations are counterproductive.
It's an issue both
(E) and
(R) have. To some extend
(E) as well, but it's not as bad for her since it transform into a stun and her ultimate actually allows her to sruvive it.
The issue with knockbacks on innitiation skills is easy: If you want to catch an out of position target you may actually put it into safety. Either way you (usually) push it father away from the team (in a normal teamfight). Transfoming the knockback into an advantage usually takes more ressources as it is worth.