The problem i find with the soit is that they hd soo many differnet varients that it is as if they couldn't get it right and had to keep changing it! were as the mustang it was develped from being the A type to the H type (with other wierd varients
The Spitfire evolved along with the continued development RR Merlin (you needed quite a different airframe to hold a 1600hp Merlin, when the basic Merlin at the start of the war developed 1030hp!), and then the Griffon (major airframe changes due to a huge leap in power and a major change in balance due to the size of the engine), not because of the design "not being right". Most of the major Mk changes were due to new engines being available (I & II to V; V to IX; IX to XII then XIV; XIV to 21 and 22).
By the time the RR/Packard Merlin made it into the P51 (remembering at the time, with reference to your point below about visibility, the Mustang was the high backed B/C), the Spit was already almost at its definitive Mk with the Merlin (Mk IX). You also make the point above that the Mustang itself had several variations - with the H model being quite a lot different to the poorly-engine P51A
Overall to me the mustang is better due to secifications such as speed manueverbility and g loads also visibilty was better and the undercarrage was far better due to it being wide track!
Yep, the wide track undercarriage is a nicety and certainly an advantage the RAF knew about. When the pressure of war was over, and Vickers-Supermarine developed the Spiteful, one of the main changes was a switch the a wide track u/c unit.
The Spit had a bubble canopy too, with the the Mk XVI (development of the IX), the XIV and all subsequent variants bar the XIX and 21.
The Spit also had a useful naval career too (as the Seafire). Another example of its versatility.