All you are telling me is that most time travel in Star Trek has been innacurate with regards to current prevailing theory, and somewhat inconsistent anyway.
All you're doing here is repeating O&K's claims about "current prevailing theory." There is no
"current prevailing theory" about how time travel would work (although there are plenty of speculations), so realistically they were misrepresenting what the MWI means in order to rationalize their story choices about how to execute a reboot.
UHURA: An Alternate Reality.
This bit of expository dialogue was, obviously, O&K's attempt to get the point across to the slower members of the audience, slightly less blunt than having the writers themselves walk in front of the cameras and say "this is what we mean." However, at that point in the story it can realistically be nothing more than speculation on Spock and Uhura's part ("alternate to what?" is the obvious question from their POV), and moreover it provides no evidence one way or the other as to the status of the "prime" universe.
If you are correct about the evidence about the fate of the "prime" universe, then we have insufficient data to test the idea that the movie portrays an overwritten/singular timeline.
Since Star Trek in general is inconsistent with it's implied portrayal of Time Travel, we cannot look to the rest of Star Trek as a guide to how it worked in this movie, so outside precedent carries no weight.
we are thus reduced to using the movie in and of itself to suggest whether it is an Alternate Reality, or whether linear time has been overwritten so that events after 2233 do not happen as depicted in the rest of Star Trek.
In order to accept the linear timeline theory, we have to accept the following:
- Cause and Effect have absolutely no meaning, since Spock CLEARLY observed and remembered events that simply can NOT happen since Nero's arrival.
Since the Grandfather Paradox comes in, the integrity of Spacetime is simply no more. Younger Spock would have different, contradictory memories to Older Spock, so when it comes time to go back in time, he may not do so, or would likely come back with something different to say to kirk, and the causality loop would go on indefinately.
Either that, or Spock would have to lie to kirk about events of the future.
Since this breaks cause-and-effect, it is thus not logical to assume this model.
Therefore, MWI must be the only logical alternative.
Given MWI, and Spock's generally analytical and logical approach, it is reasonable to assume that Spock:
a) Cannot go back in time to fix anything;
b) Relatively quickly reasons this to be true.