I see people say that often, and I don't really agree.
Because "beast mode" Crosby or Ovechkin are pretty damn spectacular themselves.
I think people are a bit wow'd by peak Malkin because how much better peak Malkin is than career Malkin. Whereas for career, peak Ovy/Crosby are closer to career Crosby/Ovy so it stands out a bit less.
ie career - Ovechkin/Crosby >> Malkin
Peak - it's closer
But - just because it's close, it doesn't mean Malkin is better. All 3 are truly fantastic at their peaks. I still take Crosby #1 myself.