The only reason to imagine that plateau is because it’s painful to imagine a near future where humans have zero economic value.
Do you have evidence or empirical arguments to the contrary?
I just find the belief that the continuous rapid improvements in machine intelligence stopping just short of human intelligence quite arbitrary.
It's a view I don't share at all. I don't see anything that could be even remotely considered intelligent under any reasonable definition of the term. Useful in places, yes. Intelligence, hard no. So the question of whether it will approch or surpass human intelligence makes no sense to me, because the technology and its progress are in an entirely different dimension and unrelated to that idea or goal.
But there doesn’t seem to be any off ramp, given the incentives of our current economic system.