I don't think they had much choice but to announce it back last November. In my view, I feel an announcement is rushed if no gameplay is shown, and that's exactly what P5's announcement seemed to be. For all intents and purposes, if we hadn't been waiting so long for P5's announcement, I doubt the game would've been announced in the manner that it had been. With that in mind, I think the manner of P5's announcement is largely irrelevant.
I don't know about that. What really would be pressuring Atlus to announce it if they weren't ready to? They wanted this long, nothing would be stopping them from waiting another few months, especially since they had PQ and the other games to hold the fans over if they wanted to wait.
They aren't a big company like Square Enix who felt the need to reveal games like KH3 at E3 just to generate momentary hype when the game wasn't anywhere close to finished.