https://www.quora.com/What-was-John-von-Neumanns-IQ-Was-he-s...
The conclusion seems to be that he had a higher raw IQ but Einstein was a 'deeper' thinker and better aesthetician. General relativity (which took Einstein 10 years of 'thought experiments') is often considered the greatest achievement of any single human mind. In Einstein's words:
"After a certain high level of technical skill is achieved, science and art tend to coalesce in aesthetics, plasticity, and form. The greatest scientists are artists as well." - Albert Einstein, 1923
According to George Pólya:
“The only student of mine I was ever intimidated by. He was so quick. There was a seminar for advanced students in Zürich that I was teaching and von Neumann was in the class. I came to a certain theorem, and I said it is not proved and it may be difficult. Von Neumann didn't say anything but after five minutes he raised his hand. When I called on him he went to the blackboard and proceeded to write down the proof. After that I was afraid of von Neumann”.
My read is he's saying for the most part mathematics arises in empiricism, in real world problems. Once the problem is translated into mathematics useful tools develop, but then over time branches will spawn that become increasingly abstract/aesthetic and are generally a waste of time.
I also liked the beginning bit where he says you generally can't understand something until you have "assimilated it in an instinctive and empirical way". You need that muscle memory, even for intellectual subjects.
[1] https://www.amazon.com/Martians-Daughter-Memoir-Marina-Whitm...