IMO the biggest problem is the freaky damage modelling.
Somehow, the "bias" in updates gives out very strange results. For instance, when the AI driven drones are lagging behind, somtimes these drones show amazing capability to withstand concentrated fire. It feels almost as if the hits on the drones aren't registered at all.
Other times, hits on the lead bomber which the player is controlling result in consecutive damages to the drones when it is shot down. I've tested this on the B-26 and found out it was true. I aimed only at the lead bomber, dumped about 50% of all ammunition on that single plane, and after it blew up, the second and third plane blew up consecutively as the pilot of the bomber was relocated.
...
Coupled with the lacking DM, this probably adds the most decisive problems on the high bomber fatality rate.
ps) However, the individual bombers are tougher than any of the fighters. Bombers are only planes that withstands more than a single round of 30mms, other than the rare case of P-38s. And hitting the intended target with the bombers is not hard. It requires a long, steady bomb run, and that is all.