Actualy the P40B has more firepower than the A6M2.
Lets take a look at the comparative weights of fire of the primary apponts in the Curent CT set up:
P40b:
Four Browning 30M2 1200 rpm / 490 rpg @ 835m/s, weight 9.73g=15.89
Two Browning 50cal 750 rpm / 380 rpg @ 870m/s, weight 48.5g=38.64
Total:54.53
Huricane MK I:
Eight Browning 303's 1140 rpm / 333 rpg @ 745m/s, weight 11.3g=26.406
A6M2:
Two Type 97 7.7mm 1000 rpm / 680 rpg @750m/s, weight 11.3g=15.368
Two Type 99 MK I 20mm 520 rpm / 60 rpg @525m/s, weight 129g=29.76
Total:45.129
C.202:
Two Breda SAFAT 7.7mm 900 rpm / 500 rpg @730 m/s, weight 11.9g=13.222
Two Breda SAFAT 12.7mm 700 rpm / 400 rpg @ 760 m/s, weight 36.7g=41.94
Total: 55.16
The Nate(Ki-27) and the Oscar(ki-43 early model) both had only Two 7.7mm MG's, so clearly they would be at a serious firepower disavantage, or rather "Firepower Chalanged.
Somthing the above Numbers do not cover is Effctive range, the US 50 cal has a tremendious effective range advantage over the 20mm and 7mm rounds on the Zero, at least 3 times the range, this being said the 50cal could acheave meaningfull hits withen an envelope at least 3 time larger than Zero's.
Another point not covered is time on target, the 8 gun pack on the Huricane can deleaver damage Four times faster than the Japanese 7mm rounds.
When I say the Allies have a fire Power advantage this is what I am refering to, compound that advantage with the Fragile Zero, and tough P40 and Huricane and you have the full picture.
The Peggy also has prety much the same bombload as any other Japanese Bomber, around 1800 pounds, so it's not uber in this since.