Except there are an ungodly number of people who can splitpush till they are gonna be ganked and then run away.
That problem is 2 fold. One, youre wasting your ult as an escape, now you contribute even less to a team fight. But you dont have your ult anymore so you cant safely splitpush anymore. Two, someone who can duel and beat 1+ people are much better splitpushers than someone who has to run with their tail between their leg every time someone shows up.
Also, most good assassins have a way to get out, Quinn does not. So if you want to compare he to those, then she still has that going against her.