just because it wasn't often done does not mean it couldn't be done.....big difference..... 
those guys were fighting for their life...we on the other hand have no such worries.
Seems like the risk of death would result in more crazy-arse maneuvering to shake the guy off your 6, not less.
And as to the origional topic, it seems to me, admittely based on limited experience flying them but a fair bit fighting them, that the primary 'issue', if one could call it that, is relatively light control surfaces at relatively high speed.
By this I mean that even at the same speeds, a spitfire will have lighter controls than, say, a 109, or a C.205. Its entirely possible that this is just perception, as I have never done a direct comparison with a spitfire. I don't even know exactly how they determine the level, or even if they just let the physics model determine it based off of surface area, deflection of the control surface, air density, and speed.
Just my $0.02.
