I fly bombers at times, and I fly fighters against bombers at times. I don't find bombers to be overmodelled or unbalancing from either point of view.
All aircraft should be modelled realistically, so I'm not in favor of any special handicap bombers should have (like reduced speed or increased fuel burn relative to fighters) just to make them easier to shoot down.
Yes, the coordination of gunners is good in AH because of one person controlling three bombers. But as the convergence is statically set, this isn't as deadly as it would be with a full complement of good gunners, which bombers never have in AH. I think it's a tradeoff, probably favoring bombers somewhat, but not enough to be unbalancing. Also, I'm not sure what alternative would be better with regard to guns. The only thing that seems likely to me is not having bomber formations. Of course, if that were done, bombers would be rare, which I think would make the game less fun.