It's almost certainly more complex of course, but the UK called it's arsenal a "deterrent" before I left, and I've heard the same for why China stopped in the hundreds of warheads.
Btw., China is increasing its arsenal at the moment.
Powerful enough AI creates whole new classes of risks, but it also magnifies all the current ones. E.g. nuclear weapons become more of an existential risk once AI is in the picture, as it could intentionally or accidentally provoke or trick us into using them.
Instead imagine a non-human intelligence. Maybe its alien carbon organic. Maybe it's silicon based life. Maybe it's based on electrons and circuits.
In this situation, what are the rules of intelligence outside of the container it executes in?
Also, every military in the world wargames on hypotheticals because making your damned war plan after the enemy attacks is a great way to wear your enemies flag.
More seriously though, Egyptian gods are equivalent to aliens in general, and adjacent to AI, and close enough to fighting a nation that somehow made a major tech leap, so militaries absolutely plan for that.
"I'm going to build a more powerful AI; don't worry, it could end the world, but it also could not."