Here's an argument for why the change in power might be pretty sudden.
Currently, humans have most wealth and political power.
With sufficiently robust alignment, AIs would not have a competitive advantage over humans, so humans may retain most wealth/power. (C.f. strategy-stealing assumption.) (Though I hope humans would share insofar as that's the right thing to do.)
With the help of powerful AI, we could probably make rapid progress on alignment. (While making rapid progress on all kinds of things.)
So if misaligned AI ever have a big edge over humans, they may suspect that's only temporary, and then they may need to use it fast.
And given that it's sudden, there are a few different reasons for why it might be violent. It's hard to make deals that hand over a lot of power in a short amount of time (even logistically, it's not clear what humans and AI would do that would give them both an appreciable fraction of hard power going into the future). And the AI systems may want to use an element of surprise to their advantage, which is hard to combine with a lot of up-front negotiation.