I agree that the fighter stats (among other things)need revision across the board. Not sure though what you mean by MGs being not too effective against bombers. Even a rifle caliber .303 could be effective against a bomber if there were enough of them, as the Hurricane demonstrated against twin engined MEs and HEs in 1940. And in most Japanese aircraft, bombers included, the lack of self-sealing fuel tanks made a/c very vulnerable to rifle caliber rounds when AP-Incindiary rounds were in the attacking plane's ammo mix. Then of course the US .50 was highly effective, not only against all aircraft but against light surface ships as well, despite the absence of an exploding shell. It had the range, velocity and weight to easily penetrate the armor on any a/c or the steel on any unarmored vessel or light tank. Certainly it was a much better weapon than the cannon installed on Japanese a/c, or the 37mm on the Airacobra.
My solution to the egregiously flawed a/c stats was to assume that the F4F is 1 MVR worse than the A6M2 and the P40 1 MVR better and adjust OBC41 (using the editor) all late war US a/c, and the Spitfire variants, upward from there. The highest rated fighter in my revised stats is the P51 with an MVR of 30. The rest: F4U 28, F6F 26, F8 27, P38 25/27 (F/J), Spitfire VIII and MVR of 27. I judged these changes to be appropriate *relative to the A6M2 stats presented by the game designers* so they are not based on any formula.
With these changes I have found that with the decent durability numbers on US a/c, the US bomber casualty rates are in the ballpark and can be left as-is. With the US fighter MVR numbers upgraded as suggested, Japanese Nells and Betties that lack escort are dead meat, and appropriately so.
My other solution was to change all at-start USN pilots to EXP 80, all USMC pilots to EXP 70, and all USAF pilots to 60. UK pilots in India and Malaysia receive EXP upgrades across the board to 70 (on the grounds that these units were more likely to have experienced pilots transferred from the ETO or to have been more thoroughly indoctrinated about lessons learned during the Battle of Britain.
With these changes I get Japanese victory ratios in 1942 that more closely approximate reality. The IJN can still still send waves of fighters against well supplied, heavily defended bases, but they lose about 1.4:1 (bombers and fighters vs. allied ftrs) when they attempt it, and about 1:1 when you just compare the fighter losses. The revision more accurately simulates the general lack of hitting power and speed of most Japanese a/c while still giving them a decent compensating advantage in EXP. I have found that with the modifications, Japanese A6M2s, Oscars, &c are easily able to overwhelm an isolated airbase like Clark, despite the presence of P40s, inflicting about 2.5:1 losses against allied pilots by dint of numerical superiority and the low initial Allied HQ preparation ratings. The Pearl Harbor raid using the historic opening move is just as devastating and the IJN losses do not change substantially. On the other hand, with my changes you no longer see 40 Oscars flying into Kunming and waxing 15-20 P40s without taking a loss.
Show me a fellow who rejects statistical analysis a priori and I'll show you a fellow who has no knowledge of statistics.
Didn't we have this conversation already?