How so?
unlikely.
And First Contact changing the timeline is an old fan theory, I’ve always liked it but it’s not canon.
not officially, but I don't see how anything works otherwise - the next show being Enterprise, which contradicted a lot of small details and lore established in TOS and TNG, and already had a built in time-war, right after a movie that rewrote the timeline from an earlier point, multiple times during the course of the movie. Enterprise had the Borg drone, and between that and Daniel's quarters, so much tech was introduced early, and the NX went from having blown up to having founded the Federation...... it all just screams, to me, of multiple butterflies coursing through the timeline. The next show is Discovery, which has a MASSIVELY redesigned 23rd century, because of all this new tech introduced to the newly rewritten 22nd century, leading to the current Discoverse, with all sorts of small details from early TOS and early TNG being contradicted on a regular basis. Its the one theory that explains ALL of the things people can complain about. Its logically consistent with itself. It allows you to watch all of the shows in production order, instead of jumping around from the 2000s to 2017 to 1966 to 1987 to 2020 to watch the show in chronological order. You can watch them in the order they were made, and the pieces all make sense, because the timeline was rewritten during FC, and then the narrative jumps back to Enterprise and starts over. It makes the franchise whole, and the only good TNG movie is the lynchpin that causes the rewrite and holds the whole thing together. I can go with it. And if it can retcon Generations out because the timeline was rewritten afterward?? DO IT BEFORE IT IS TOO LATE.
As for my other point, Spock isn't perfect, and didn't expect red matter to open a dimensional and/or time gate, and if both were involved, he may only recognize the one element. Instead of having to handwave "changes went backwards!" to explain all sorts of differences, and to keep it consistent with the way alt Us and timeline rewrites have been in about 95% of the franchise, it just makes much more logical sense, to me, to declare it a pre-existing alternate universe. IMO, YMMV.... if it was just time travel, then the Kelvinverse would be literally existing in the fabric of what used to be the Prime universe; it wouldn't have spawned another one. There isn't a world where the Nazi's still won WWII, and one where the whale probe destroyed Earth, and one where the Klingons destroyed the D, and one where the Borg took over during the 21st century. It defeats the point of all those episodes and movies and gets rid of any drama or weight the stories may have held, let alone the fates of the people left in the "bad place", and the hollow victory of our heroes who "saved the day" only to escape to a new place, leaving their old one behind. The Prime Universe wouldn't exist for all of these shows to be happening in. Now, if they make one more Kelvin Trek that closes the loop and resets to a version of "Prime" by stopping Nero before the Kelvin is destroyed, then I repeal my entire rant.