F3 view makes sense in LEVEL bombers for two reasons:
1. They must spend a significant amount of time out of the cockpit - be that in F6 view calibrating and fine-adjusting the flight path, or in a gunner's seat tracking a fighter that is waiting for his chance to swoop in. F3 allows them to quickly track the aerial threats around them and get back to F6, pilot seat, or a particular gunner. F3 helps them to do the job done by at least 3 different people in a real bomber. Planes like A20, IL2, SBD etc. do not use a bomb sight and do not (really) rely on a gunner for defense - they rely on maneuverability which is done from the cockpit. Yes they had a second crew member but so did the 110 and the Mossie and I see no justification for F3 view in their case - nor there is one for A20 and IL2.
2. Level bomber tend to be heavy, slow and take a long time to climb and cruise to their targets. During 90% of this time there is nothing to do except talking smack on channel 200 and admiring the beauty of your plane from F3 view. A20 does not climb high is faster than a few fighters and its typical mission profile does not take it more than 1 sector away. I bet that in a significant % of its sorties it never loses sight of its takeoff base. There is less need of entertaining yourself in F3 view.
I am sure that HTC could master their great coding talent and allow an additional flag added to planes of the bomber category that enables/disables F3 view per plane. This way IL2, A20, SBD, Stuka et al. could roll out of the BH and still have F3 disabled.
The rule of thumb should be: no level bombsight = no F3 view.