Consider a world in which AI existential risk is real: where at some point AI systems become dramatically more capable than human minds, in a way that has catastrophic consequences for humanity.
What would you expect this world to look like, say, five years before the AI systems become more capable than humans? How (if at all) would it differ from the world we are actually in? What arguments (if any) would anyone be able to make, in that world, that would persuade you that there was a problem that needed addressing?
So far as I can tell, the answer is that that world might look just like this world, in which case any arguments for AI existential risk in that world would necessarily be "very hypothetical" ones.
I'm not actually sure how such arguments could ever not be hypothetical arguments, actually. If AI-doom were already here so we could point at it, then we'd already be dead[1].
[1] Or hanging on after a collapse of civilization, or undergoing some weird form of eternal torture, or whatever other horror one might anticipate by way of AI-doom.
So I think we either (1) have to accept that even if AI x-risk were real and highly probable we would never have any arguments for it that would be worth heeding, or (2) have to accept that sometimes an argument can be worth heeding even though it's a hypothetical argument.
That doesn't necessarily mean that AI x-risk arguments are worth heeding. They might be bad arguments for reasons other than just "it's a hypothetical argument". In that case, they should be refuted (or, if bad enough, maybe just dismissed) -- but not by saying "it's a hypothetical argument, boo".