Bear in mind, development of the Spit began in 1936 where biplanes still ruled the air, the Spitfire itself a huge leap in design. The Mustang started development something like 4 years later, that's eons in technological terms.
As an example of that, the Mustang was scarcely on the drawing board when the Spitfires were engaging the Luftwaffe in the Battle of Britain.
Another example of technological advances vs time, my dad, airframe fitter from about 1949 said to me one day (talking about his time with aircraft) , advances come along so fast, it was bewildering, you were constantly challenged by new aircraft, technology etc etc.