Let's not forget that when the Hurricane was designed, inside Hawker it was called the "monoplane Fury", a.k.a. what is the least-effort path to convert the Fury to a monoplane? And in the end, they achieved not only that, but they added a retractable landing gear, an enclosed cockpit, upgraded from the Kestrel to the Merlin, and installed a much more powerful armament with 8x.303's. That's quite a few major improvements all in a single generation!
I think it's unfair to criticize the Hurricane for not having aerodynamics on par with the Mustang, a plane which wasn't even on the drawing board by the time the Hurricane was already in widespread service. As for retrofitting a Mustang-style radiator to the Hurricane and other aero improvements, well, as mentioned that's more or less a redesign. And seems Hawker was pretty occupied by the Typhoon/Tempest at that time, from where would they have gotten the resources to dedicate to improving the Hurricane? Or IOW, improving the Hurricane would in practice have meant delaying the latter aircraft, maybe not a worthwhile tradeoff (well, given what a trainwreck the Sabre turned out to be, one could argue that designing aircraft powered by anything else would have been a good choice..
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