I think the point is that Feynman came later to contribute to Quantum Electrodynamics, the "first theory where full agreement between quantum mechanics and special relativity is achieved."*

* https://en.wikipedia.org/wiki/Quantum_electrodynamics

Feyman was too young for the really fundamental work on quantum mechanics. He won his Nobel prize for his work on quantum electrodynamics. However, he created the path-integral formulation of quantum mechanics, which can be thought of as another way of describing quantum mechanics.

It's worth mentioning that the path-integral formulation had a seed in Dirac: http://en.wikipedia.org/wiki/Path_integral_formulation

yeah, I was thinking, uh, the path-integral formulation?? Which IIRC is still kind of mathematically ill-defined, but still.

making a fundamental discovery is not necessary to be a 'great mind', I think. As the man himself said, 'what I cannot create, I do not understand'.

Yes, echoing the others Feynman was too late for the foundational, completely change your view of the universe stuff.

Gamow's Thirty Years that Shook Physics: The Story of Quantum Theory http://www.amazon.com/Thirty-Years-that-Shook-Physics/dp/048... is the standard non-specialist account of this, it starts with Plank right after the turn of the century and is essentially complete in 3 decades, about when Feynman was in high school and teaching himself serious math.