Well, if you shoot at the A-spot, you can't get to an open space without getting hit, making that spawn exit useless:
B-spot might be even more annoying coz it cancels access to main road and squeaky door from both spawn exits. Well, ok you can enter that house via window jump too but I don't see many ppl doing it.
But in the end, the whole Venice 2nd phase heavily disfavors Allies. You'd need in previous map like 300-600 better ending score than Axis to have a proper chance. I think this map has like 10% win rate for allies. The problem is that every route for allies is a bottleneck or has a long, slow swim. Combine that with huge teams and the lethality of bottlenecks is multiplied. If Axis is able to setup heavy weapons, arties, snipers and crossfires at each bottleneck, it's pretty much game over for allies.