I think it's easier to aim with some sort of optic than it is without. Not faster, but easier and certainly more accurate too.
Irons require you to line up the front and back sights with your target, whereas any sort of optic only needs you to line up the optic's crosshair. That's lining up 1 thing with the target instead of 2, which is an improvement, it takes less time and doesn't require you to position yourself in a certain manner to look down the weapon properly.
Additionally, BBs can be seen in flight. Having a zoom allows you to see them in flight for longer, meaning you can see what happens to them and adjust your aim if need be, better, than if you were using irons.
I've actually noted before that when a team has had a few people with ACOGs or similar and the other team have had irons only, the team with the optics has won. I doubt this could be applied to every situation, but I've witnessed it and remember taking note at the time.
I think a lot of people get caught up by the thought of real assault rifles tending to have 4x or less zoom optics. If a real rifle powerful enough and accurate enough to kill someone at 600m + and only needs a 4x ACOG, then by comparison, airsoft shouldn't need optics, right?
Well, yes that's a fair point. But it's irrelevant, airsoft isn't real and there's no denying that being able to get a closer view of things without physically being closer, is an advantage.
Conclusion?
If you want a scope, use one.
It has to be said that huge sniper style scopes with variable zoom are daft to use on an AEG though, you can't sight in fast because of the eye relief and they're simply unwieldy for the task, as well as having a quite narrow field of view when fully zoomed.