...2. Trek has used both "our timeline was changed" and "we created a new timeline" versions of time travel.
Trek has never said that a new timeline left the original intact.
It's always been said the one original timeline was changed.
Please give me an example of even one episode where they felt a new offshoot timeline resulted from the past being changed.
If that'd ever been said, the characters would have been stuck in the offshoot, with no way of EVER getting home, since changing the past a second time would only have created a THIRD timeline, not returned them to the original.
...One of the ones that comes to mind is "All Good Things," where the presence of an anti-time thingermajiggy creates three separate alternate timelines that all diverge from one-another yet co-exist...
That was nothing but Q messing with things, and had NOTHING to do with normal time travel.
Give another example. One that doesn't involve a being that can alter the fabric of the universe or put the starship Voyager inside someone's Christmas tree decoration.