Somewhere there's a reference that lists each rounds destructive power in game, relative to a single M2 .50 cal round. If I remember correctly, a P-47 with 3200 rounds of .50 cal can knock down a single hangar with simple MG fire only. In my experience, it takes 4 or 5 long passes with convergence set to D650 to do it, as the hangar hardness is something like 2800 or so. 6 5" HVAR is roughly equivalent to 1000 lbs of bombs, since HTC models the weight of the rocket (~150lbs) instead of the HE value of the warhead (5" Naval HE round of 40-50 lbs of explosive). I don't know the destructive value of the N1K2 20mm in game, but its probably somewhere in the area of at least 3 times or more of the .50. So the 900 rounds the N1K2 carries is going to be roughly equivalent to 2000lbs + of destructive power in game. Couple that with the bombs it carries, and you have roughly 2500-3500 lbs of destructive power on a single N1K2. An F6F can carry 2000 of bombs and ~ 1000 of rockets, plus the .50 cal, so you're pretty close. An F4U-1D gets two extra rockets, so its 300 lbs better than an F6F. P-51D has roughly the same as the F6F.
My math gets pretty screwy here since I'm working off a lot of approximations, but unless I've grossly over or underestimated something, you can see that they're all pretty close. Only when you get to the aircraft like the Jug that can carry 2500 lbs in bombs plus 10 rockets and guns can you get into a severe difference in the ordnance capability. Obviously the F4U-1C with the massive load of 20mm and bombs/rockets would be even greater.
I'd have to crank up a spreadsheet with the exact numbers to do this properly, but hopefully you get my drift.