In the end it’s really irrelevant likely because notionally the same “people/pilots” would form the negotiating committee, lec’s, mec’s, and ultimately the same pilots of A.A. would vote yea or nea.
Maybe the best argument for alpa is access to their pro’s who know how to analyze what the company may be able/likely to give but I’m not sure that apa doesn’t already employ similar people familiar with AA.
Everybody likes to blame alpa/apa did this or that but in the end each is just a reflection of the individual pilot group they claim to represent.