Wait, do you really think they're throwing these games together that fast? (although, with the state of Unity I guess it's not that preposterous an idea, haha) For real though, Ubi Montreal has multiple teams. They work on multiple games at once, even multiple AC games within Ubi Montreal for a while (I think they started making AC 3 after AC2, brother hood & revelations were more iterative follow ups that didn't take as much time). This is just how leap-frog development works. Quebec has been working on Victory since before Unity came out with all it's issues (a lesson I hope they learn from before release, obvi...)
Ubi's Quebec studio has been working on Victory for more than a year though, I think they started not long after AC3, because the producer on that game is the head of the Quebec studio now... Montreal's AC team is (hopefully) fully dedicated to fixing unity as quebec is working on this....