I agree. Generally I only ask that a show/movie set its rules and not violate them. I prefer it when it's based on real (if theoretical) science. But I'll play along with world building. It's one of the reasons I don't mind the nonsense of Back to the Future. The idea of the kids disappearing in birth order is dumb as shit (not to mention the fading of Marty's hand). But they set rules and they abided by them.
This show has been pretty consistent. As I said above, the multiple time threads theory sort of lowers the stakes for the team since it would not have affected them if they stayed in their own thread. Sybil is wreaking havoc on the multiverse at large by creating new chaos streams. But nothing that has happened can be changed (somewhere the Season 5 dystopian blown up earth future still exists, just sans Deke). It just makes another thread.
I guess you could argue that the heroes were driven to prevent the creation of new dystopias. But if you start down that road, you're playing multiverse whack-a-mole.
As a side note, I admit that will draw some sort of abrupt lines sometimes. Watching Pacific Rim, I was 100% on board with giant robots fighting aliens. But I was super annoyed by the four propeller helicopters carrying the robots. The physics of that just didn't work. So, utter nonsense based on ludicrous BS? Fine. Violating the laws of real world physics? Instant cognitive dissonance. Just give me a bonkers explanation please. I will absolutely buy in.