It's a good idea. Even as far as the Defiant was concerned as far as I see it's a good idea killed by poor tactics (or, for example, the addition of a single or even two forward-firing wing-mount guns might have saved it).
I can't see why this idea wasn't used more often for bomber-destroyers though. I remember the old Il2 where I used to fly a B25 from the top turret without any payload and cut down fuel (for speed purposes) and use it to shoot down bombers. The B29 was even better for it on the servers that allowed all aircraft. You could hunt down other B29's, then use the 4 .50's in the front turret to bring them down. Happy days
