That's interesting - first time I'm hearing the idea there might be an intelligence ceiling around the human level. Who talks about this more?
It is an open question and typing "human intelligence ceiling ai" into your search engine of choice is a good way to see that, but it is basically wishful thinking. The likes of David Deutsch, Judea Pearl and Noam Chomsky all argue this at differing levels of academic integrity (IMO Steven Byrnes has produced the most rigorous work on the English internet), but there is a simple objection.
If you have a single AI that is capped at an intelligence ceiling equivalent to human levels of intellect, what is stopping you from running fifty of them, in parallel, at fifty times faster than our normal human clock speed, as a team?
But consider, in the alternate universe where we never invent AI, economic p(doom) is also 100%. Humans are fragile and short-lived.
https://youtu.be/b5z5R6xqEG0