Wasn't faster than the Spitfire IX at combat altitude, though, was it?
The point was comparison to the 190 and Typhoon, not Spitfire IX. And while the performance at military power for the Mustang I and IA may have been less, with WEP (or overboost prior to formal WEP rating) it's a different story below 10,000 ft. (especially below 6,000 ft) The Mustang II/P-51A was in the same boat comparing military to WEP, though with higher FTH, not as much power down low and critical altitude for level speed just above 10,000 ft.
Might have is guesswork, not history.
Bigger issue is the RAF simply disliked the P-39, they employed overboost plenty on P-40s, so it would have become relevant had they adopted the P-39 more heavily.
It didn't; the Merlin XX was as big an engine as it could take. The Hurricane was also a deathtrap for pilots, if the wing tanks were holed, since the cockpit's open framework drew the flames straight in, and onto them.
Weren't solutions for that already employed on later Hurricane models? (including firewalls)
And my comments regarding the Hurricane were also largely regarding its continued historical production for practical/volume reasons and possibly compromises to improve the design without totally shutting down production. Hawker also had Gloser, and if not just building more spitfires, Gloster's F.5/34 design had better drag characteristics than the Hurricane and high speed handling characteristics than the Spitfire plus better cockpit visibility. Hawker putting more resources into developing a Merlin powered derivative of that design may have supplanted Hurricane production. (A Taurus version would be bad in hindsight given that engine's problems and the weight of the Hercules might make it tougher to adapt than the Merlin, but perhaps worthwhile as well)
That of course, aside from twin-engine development, which is the only other practical option for heavier fighters with the Griffon not available sooner and the Saber unreliable.
How about the P-39's sudden and deadly flat-spin?
How about the Corsair's reputation for being fatal to new pilots?
Both of those were seriously problems that should have been caught earlier in testing and addressed sooner in the P-39's case, and seriously limited the Corsair's carrier suitability in general. Though, in both cases, I do wonder if wing slats (or even fixed slots) would have been worthwhile solutions. The P-39 may have had other solutions including nose ballast, but I believe tip-stall was still a bit harsh regardless of actually entering a spin. (and one of the issues complicating landing on both aircraft)
In the F4U's case, with the carrier landing requirement, wing slots ahead of the ailerons might have been enough to address the dangerous tip-stall and wing dropping tendencies. (take-off and turn performance may have improved as well, though at the expense of some added drag -at least in the case of fixed slots)
Other than that, the problems with the F4U as a useful carrier aircraft also should make it one of the more attractive potential export designs. (a land based Corsair in place of the Typhoon would have been extremely useful both as a counter to the 190 threat and especially adapted into the fighter-bomber role)
So we cancel the Typhoon and what shall we challenge the Fw190 with in a low-level fight? Surely not the Hurricane...
Again, Merlin XX powered spitfires. Less/no need for the cropped LF Mk.V as well. (putting those cropped merlins on Hurricane ground-attack aircraft may have been more useful)
And without the Typhoon, there would be no Tempest...
Unless development continued and only production was canceled. Including potential Griffon powered derivatives (possibly sooner) if the Sabre was canceled and Griffon expedited.
As above.
Given the problems that the Fw 190 encountered in early operations and development, should that have been cancelled too? Same for any number of WW2 types.
No, but using alternate engines certainly wouldn't have hurt, especially during the prototype stage. A DB-601N or E powered 190 prototype may have developed to totally supplant demand for that engine with the 109 once production could switch over in large enough volumes.
The landing/ground accident rate on the 109 was higher than the 190 as well as being more difficult to fly and having poorer cockpit visibility, and short of altering the 109, the 190 makes an attractive replacement for those reasons.
There doesn't seem to be a lot between the P51A and the Typhoon, but the P39 didn't come close to the Typhoon. I know of one test which gave the P51a a remarkable speed but that was factory fresh with specially sanded finish. With normal wear it seems to have a speed of approx. 370 at about 4 to 5000 ft. The Typhoon seems to have similar performance.
The Mustang I should be faster than the P-51 at low alt, but I haven't seen any formal reports actually USING WEP in tests as that rating came later. (akin to WEP on the P-40) The P-51A's figures do include WEP though, with critical altitude for 1,480 HP at 10,400 ft at which height it managed 415 MPH, and 380 mph at 1000 ft. (the earlier 8.8 supercharged Allison of the P-51, A-36, and Mustang I should have given significantly higher speed at that level under the same conditions up to around 5,000-6,000 ft -I'm not positive exactly where the power curves converge)
The A-36/P-51/Mustang I should also have been better at V-1 chasing than the P-51A or P-51B all using WEP/overboost.
First and foremost I do believe that the GA role is the issue for the Typhoon. It had limitations as a fighter but it was the RAF's main GA aircraft. Understandably A lot is made of the A36 as an attack aircraft but I always have one question in the back of my mind and that is, if it was as good as its cracked up to be, why didn't they carry on building them? presumably there was a reason.
Not as good for GA as the P-47 and merlin P-51s were more valuable as escorts.