It's more about the guns and hitting distances in this game, rather than a problem with the plane itself IMO.
What if people can't hit worth crap outside 200 yards like its supposed to? Then even a small advantage in speed would be enough to justify flying a faster plane over a Spitfire. However, in AH the firing distances of average grade pilots are commonly as far out as 400 yards, with some great marksmen shooting out far as 600~800 yards to bring enemy planes down. Me, I've personaaly been shot down countless times by 50cals from more than 600 yards out, upto about 800 yards max.
Ofcourse, this is an improvement when you think about AH1. In AH1 the hitting distances were even further out, 500~600 yard shots were the norm where a casual spraying of cannons at distances would still have a high probability of bringing enemy planes down.
Compared to AH1, the pilots who fly other planes nowadays have it easy when fighting planes like the N1K or the Spit. In the old days, the slow speed of the Spit didn't matter much. Just a little bit of alt advantage, just enough to bring you upto 500~600 yards distance and bam, easy kills. It wasn't uncommon seeing people land some 10~20 kills in a single sortie with planes armed with either Hispanos or 50cals (or both!) back then.
But anyways, the hitting distances in the game are still more than twice of that in real life. This means people who are fighting planes like the Spitfire has to always reserve enough E to stay at least 400~500 yards away from it at all times - especially if you want to drag it into a vertical and grab a decisve advantage over it.
But what if 200 yards was enough? What if being over 200 yards was enough to stop worrying about "sprays" or "sniper shots"? Then I'd bet the Spitfire wouldn't be hated this much. Getting inside of 400 yards isn't so hard with any Spitfire in the game. However, getting really close, inside 200 yards, isn't so easy in Spitfires against much faster planes.
If that be the case then I think the Spitfire wouldn't be so much as popular as it is now. What's the use of a superior maneuvering plane, if it still isn't fast enough to really bring yourself into optimum firing range?