Youngest graduates of S.H.I.E.L.D. academy ever, invented Hard Light technology around the same time that Stark did, and figured out time travel by themselves, unlike Tony Stark who did it once he got the idea of using the Quantum Realm, and they canonically did it before him. They're also two of the smartest people in the MCU 616/199999 timeline, and if you put them together, it probably beats out Tony Stark.
Are Fitzsimmons smarter than Tony Stark?