Well, enjoy the timeline while it lasts, kids, because one of those things that wouldn't be changed is that probe losing contact with the whales. And since it's doubtful that "Space Seed" is still gonna happen, or at least in the same way, therefore it's doubtful that any of these guys will be in the same position our guys were in at the point of ST IV, so they won't be in a position to save Earth. And according to these guys, the slingshot maneuver probably won't work anyway, so in about twenty years or so, Earth's gonna be an ice cube.
Enjoy.
As for the convoluted rationalization, yeah, it's an attempt to pander to crusty old farts like me by shunting this whole endeavor into an alternate timeline, and thus make it more palatable.
The problem is that I have no use for alternate timelines that have no real connection to the primary continuity (I really don't like the term "canon" and try to use it as sparingly as possible).
So, I feel no obligation whatsoever towards this flick.