Some really good posts here, lots of information to mull over.
But after the dust settles, since this is essentially a gameplay issue and most players SEEM (fingers crossed) to want relatively realistic play as opposed to arcade or what might have been possible --
why not just limit bomb release in heavy and most medium bombers to level only, within something like plus or minus 5 degrees as others have suggested?
Exceptions would be multi-engine aircraft designed to include dive bombing, e.g., Ju-88.
Even though there were issues with some planes, I assume most people would not object to allowing dive bombing from all single engine aircraft.
This fix seems relatively easy to do. Isn't it time to do it now, at least with debut of Aces High II?