Which is why I said "If the Tempest had been called Typhoon II, which is what Hawker originally planned to do, would you be saying that the Typhoon was an airframe 'that could do more than one thing' unlike the Hurricane?"Yes and no. The Typhoon was an entirely different aircraft design in relation to the Hurricane, thick wing or not.
The same can be said of nearly every other mainline fighter of the war. The Ta-152 was significantly different from the 190A, the Yak-3U was very different from a Yak-1, P-51H had no commonality to the A besides name, ect.The fact that the Spitfire had almost every part altered shows that it had growth potential. The Mk.21 had a new wing but that only entered operational service in January 1945. Prior to that variant, all Spitfires had adaptations to the same basic wing form. Again, that's growth potential intrinsic to the design. Singling out the Mk.21 or P-51H completely ignores the growth inherent in both original airframes.
In order to have the capacity for growth, you must first have a design that doesn't just barely do its primary job. It must have the structural integrity to absorb more powerful engines, more armament, or take on different roles...and remain competitive while doing it. Some aircraft have those attributes and some don't. The Mosquito is another example of a type that did have growth potential...while the Blenheim is a type that didn't.
What made an aircraft have growth potential was being a good enough performer/cheap enough/in production that it had the engineering manpower sunk into it to make it better.
Thats the point.The P51D was a totally different aircraft to the P51A, the P47N was totally different from the P47C, Me109E and 109K ditto FW190Ato FW190D, no pre '42 aircraft were the same as post '44 models.