I remember an interesting link on WWII gun effectiveness;
WWII Gun Effectiveness
Basically, the 30mm round from the MK108 has around 60 times the stopping power of a 0.303 round from the British MGs, and about 5 times the stopping power of the MG/FF 20mm rounds. Even the 8 gun wing of the Spitfire and Hurricane was less that 1/4 as damaging as the single MK108 in the nose of the lat war 109's. The four HS.II in the wings of the Typhoon and Tempest were six times as effective as the 8 gun wing, and even though the MG151/20 didn't have quite the stopping power of the HS.II, the 190's 4x20mm and 2x13mm was still five time more destructive than the 8 gun wing. even the six gun US wing was twice as effective.
Number of guns aside, these were not heavily armed fighters.