I agree with your point about the validation bottleneck becoming dominant over raw compute and simple model scaling. However, I wonder if we're underestimating the potential headroom for sheer efficiency breakthroughs at our levels of intelligence.

Von Neumann for example was incredibly brilliant, yet his brain presumably ran on roughly the same power budget as anyone else's. I mean, did he have to eat mountains of food to fuel those thoughts? ;)

So it looks like massive gains in intelligence or capability might not require proportionally massive increases in fundamental inputs at least at the highest levels of intelligence a human can reach, and if that's true for the human brain why not for other architecture of intelligence.

P.S. It's funny, I was talking about something along the lines of what you said with a friend just a few minutes before reading your comment so when I saw it I felt that I had to comment :)