I would say that a war like that suddenly coming up isn’t that insane. In the real world I think about Desert Storm.

Short armed conflict, lots of Americans and Iraqis died. Did it to fight a dictatorship. But 10 years later by it wasn’t a thing that just came up every day on the news. (Iraq 2 notwithstanding that suddenly made it all the more relevant). But my point is that there was a war in the 90s that affected a ton of people but after a while, it wasn’t constantly in everyone’s mind.

Is it a big change, absolutely. But so were the Klingons makeup in The Motion Picture, and the Klingons being good guys.

But if suddenly no women were allowed in starfleet or slavery was cool as long as its XYZ race, that would be a continuity change that affects the world not in a retconny way but in a way that fundamentally changes the kind of show that it is.

If you want to make a sci fi show where Earth has been taken over by sexist slavers to tell a very compelling and gritty story about human nature, maybe dont make a Star Trek show.