I never said that there is any real DPS gain in an ideal situation where you don't miss skillshots, but realistically it's possible to miss a line skillshot and it's considerably less possible when that skillshot becomes a 90 degree cone that can be fired while jumping with high(er) reliability.

Evolving W technically does increase AOE dps despite not increasing Singular Target DPS, though my main argument goes back to the fact that it's a lot easier to land W in the first place (after all, missing gives 0 dps). Furthermore landing an upfront slow mid air before you even have to land your auto attack will inevitably lead to higher dps position-wise, and being able to reproc the slow after using ultimate is also a pretty big deal.

There's also the whole wave clear thing and outplaying people thing with an aoe slow.