The film lost it's original Director and Singer did rewrites. It has changed since Vaughn left, no doubt about it. There was also studio talk about Days Of Future Past before FC.
I just don't see it that way at all. Avengers is literally it's own series apart from the other stand alone Marvel franchises. Dofp is not, and the X-Men won't be coming back every three years to star in a DoFP film. It's part of the same X-men film line and that's all that has ever been there. Doesn't matter if the decade or cast is different. I get what your trying to say I just disagree. I think they are def trying to pull something similar in terms of the size of Avengers here, and that Fox is aching to cash in. It's just not the same situation in terms of how these films are set up or crossed over at all. X-Men post X3 are just going back in time. Thats not 4 films coming togther to star in an all new title. There are no crossing over of different characters from multiple stand alone series and no new series title or anything like that. I hope they go that route later post DofP, but for now none of that exists.
But yeah, think I'm going in circles now so agree to disagree haha.