under gunned..
I'd trade in the MK108 30mm and both MG131 13mms for just one Hizooka as a hub cannon.
...
Generally, it is because the guns hit out pretty far than average instances in AH. Spitfires rarely have a chance to get within 300 yard ranges of faster fighters, but given enough E advantage they can outmaneuver most planes and aquire a very, very long shooting opportunity from 300 yards to as long as 800 yards. A typical engagement would be a Spitfire(or a N1K2) diving from above, getting within about 400 yards, and then sniping the target out of the sky between 400~600 yards range.
As a comparison, the I-16 type24 in IL-2 servers out-turn almost everything else, and also has good fire power - an awesome plane to fly.. but since they rarely can get within 200 meters of the target, and since it's very very rare somebody gets hit from shots further than 250 meters in IL-2, nobody complains about them. Naturally, nobody uses them unless they are limited to it as in 1942 servers where VVS choices are the Yak-1, Yak-1B, I-16s and Yak-7.
Frankly, the whinings about N1K2s and Spitfires is really about the gunnery modelling thing, not about their performance. If the A6M zero had two Ho-5 cannons, everybody would be putting the zero in the 'dweeb plane' list in AH. Alternately, if gunnery 'feel' of AH was something like IL-2, I can guarantee 100% that nobody would be complaining about Spitfires and N1K2s.