The "Prime Timeline" doesn't actually exist.
I think fans are making a distinction that exists nowhere except inside their own heads.
There is no a single cohesive overarching "prime" universe. Whether fans want to admit it or not, TMP was the first Trek reboot. The next film, TWOK, was another reboot. There is almost no reconciling Nick Meyer's Trek with Gene Roddenberry's. In Nick Meyer's Trek, Starfleet is unapologetically full military and Klingons have pink blood. TNG was Roddenberry rebooting himself, and the other spinoffs are derivative works created by other people
. Fans consider all of this one vast universe only by ignoring the myriad contradictions between the various visions of the various creators and producers.
Abrams vision of Trek is no more or less valid than Nick Meyers'. And I say that as one who is not
a fan of the Abrams movies. Let's just stop pretending that every derivative work of Trek to ever hit the airwaves or movie theater is all one unified whole. It ain't. It's no more one unified whole than the original Sherlock Holmes stories, the movies with Basil Rathbone, the new Sherlock with Cumberbatch, and the animated series SHERLOCK HOLMES IN THE 22ND CENTURY represent a unified whole.
I think the problem is -- and no insult is intended to anyone -- that some fans who call themselves Star Trek fans are really "Rick Berman Trek spinoff" fans. That was merely one
vision of Star Trek; it had its day mostly in the 1990s, but that day is done. Star Trek needs to move on.
Again, I don't like the Abrams films, but I'm hopeful someday for a good
reboot, with no baggage at all from any 1990s derivative TV series.