Yeah I really don't see both these films opening on the same week. They will eat at each other. Batman and superman will be the victor just because holy fuck those two are in a film together finally, but both would benefit much more from being spaced apart
Avengers was huge, but I don't see these cap films getting a boost nearly as large as Iron Man 3 did. Thor 2 for example just did alright and I imagine that's a bigger series than captain America. Rdj stark da gawd. They really need somebody as charismatic for phase 3
Thor 2's gross shot up 50% (ish) over the first one, and Cap 2 is already trending for an opening weekend bigger than Thor's.
They're not getting the IM3 boost for sure, but they're still doing really well.