What makes this an alternate universe as oppose to a severe change in the timeline of this universe? Just because the writers have said it? I'm afraid not mate...
The writers are actually in a very good postion to say what happened in the movie since they wrote it
. Fans, people posting on a message board, casual viewers...none of them has any say in what happens in the movie, only the people that made it do. And if the writers say the new movie is an alternate reality and the original reality is still out there untouched then how can we argue with them? It's their
And even if it were proven to be an alternate universe, that means one thing, the Star Trek franchise is dead, there is no more of the 'Prime Universe' as you describe it, only this new franchise in what you're describing as an alternate reality.
The "Prime" universe was already
dead. The TOS crew are too old to make new movies, The TNG movies are over and done. DS9, VGR, and ENT were never
going to return in any form.