You're interpreting everything after First Contact and the others as changed timelines when the intent is that they were predestination paradoxes. There obviously had to be an original timeline prior to the various loops beginning, but IMO we never saw it.
Well, you just argued my point for me. If there was an original time line that had not been altered yet, chances are we were looking at it prior to First Contact. However, you feel that the Borg traveling back in Earth's history had already happened (as a traditional predestination paradox). Which would mean that the temporal incursion at First Contact had already happened before Picard went back in time. But how do you know that? We never saw any hint or clues to this effect. There was no evidence prior to First Contact that suggests that the event at First Contact was altered by time.
So you may say you never seen the Original Time Line prior to First Contact. But I say to you that we never seen the Pre-destination Paradox prior to First Contact (the film) either.
However, we do see that the events of First Contact have in fact effected the time stream afterwards, though. Which would suggest that we are now looking at the changed time line.
Now, lets say for the sake of argument that First Contact was pre-destination paradox prior to the film (as it is normally defined):
What about the technological advancements we see on Star Trek: Enterprise? The temporal cold war had not involved the humans in Broken Bow just yet. So their time line shouldn't have been altered by it yet. This leaves the explanation that Picard and crew had in fact influenced their own time line. Which in effect, caused man to advance more technologically quicker.
Why didn't Cochrane seem surprised or make a comment about Kirk being from a ship called the "Enterprise". I mean, it is a rather large coincidence. I don't think he would have not said anything or not have some type of reaction when they said the name Enterprise.
We've had proof that the Enterprise timeline was changed by at least two big events ("Shockwave" and the Xindi attack), but the way I see it nowadays, TOS, TNG and the rest are all the result of this tampering.
Enterprise was changed by the Temporal Cold War in the beginning of Broken Bow. The time line was altered by genetically enhanced soldiers (Suliban) taking orders from someone in the future.
Don't get me wrong, you can believe what you want and there is loads of evidence to support your claims. Owing to the way the multiverse theory works you could argue an episode takes place in an alternate universe where the only difference is that Uhura applied her socks left-first instead of right-first today. Where do you draw the line between continuity errors and alternate universes?
Within the context of the universe: there are no continuity errors. There is a reasonable explanation for everything within Star Trek. The most ridiculous of scenes or moments can be explained as practical joke by a Q or some higher powered being. Other blunders can be explained that it was a change within the time line (that is if there was a recent temporal incursion). Why do I bother explaining the errors on the series when I know they are actually mistakes? Well, why bother to believe in warp drive when I know it isn't real? For the same reason I choose to suspend disbelief in a fictional universe in the first place. I want to enjoy the story and the richness of it's universe (without letting reality or continuity errors ruin my enjoyment of it).
I mean, the way I see it, why spoil the fun?
I just take a more relaxed view of continuity gaffs, broken reverse-continuity and the rest.
Yeah, I imagine a lot folks just ignore them and view them as for what they are or what they should have been.
However, part of the fun for me is to explain away the stupidity and validate everything that is within the Trek-verse (even Paris and Janeway's intimate moment together as lizards) .