I strongly disagree. USAMO problems range in difficulty quite a bit. I can solve some but certainly not all. Not so for IMO. And nowadays I generally solve all

I strongly disagree. USAMO problems range in difficulty quite a bit. I can solve some but certainly not all. Not so for IMO. And nowadays I generally solve all of the Putnam problems in the time allotted. By the way, the early years of the IMO were very easy, by today's standards (only a few countries were involved at that point). They would probably be approachable to people comfortable with the AIME problems.