This whole "debate" about "time travel rules" solves itself if we just assume it's a lot easier for our heroes to say "We need to fix the timeline" instead of what they actually mean, such as "we need to go back in time and change things in such a way as to create another alternate quantum reality that's close enough to the one we prefer and return to its future."
Once
Parallels was broadcast, pretty much all bets were off. "All possibilities that can happen do happen in alternate quantum realities."
It does not matter if Nero came back via Guardian, Red Matter, DeLorean, Elton John Air Boat, Atavachron, slingshot, or TARDIS -- the nanosecond he arrived, it was a different quantum reality.
On 2233.04, there were two possibilities: 1. A pissed off Romulan from the 24th century would arrive and destroy the Kelvin. and 2. A pissed off Romulan from the 24th century doesn't arrive and the Kelvin goes on its merry way.
Per previously established canon explanation in
Parallels, an explanation verified by the events in that same episode,
at least two quantum reality paths existed on 2233.04 -- the Prime quantum reality, and the one in which Nero arrived. In the case of the 2009 movie, the cameraman and the rest of the production staffed chronicled the events of the latter. It's as simple as that.
Add to that -- the writers, who are the people in charge of the physical laws of the Star Trek multiverse (e.g. God,, Fate, Time, Subspace), stated that
Parallels is the explanation.
Period. End of story.
)
