Koty you are right, but the Defiants were not used that way; their tactical doctrine did not allow for the pilot to fly like a fighter and use the turret turned forward, that would not make any sense at all to strap a heavy turret with 4x .303 machine guns on a single engined fighter if you already have two fighters that carry twice the punch without a heavy turret and a heavy second crew member...
so the RAF wanted the Defiant to be used like a siege turret of sorts against Bombers while the Hurris and Spits tangle with fighters;
of course it did not turn out that way;
but again, the doctrine did not go for the pilot using the turret moved forward...
btw, with a competent AI gunner, this could work; I have shot down quite a few enemies (or better gunners in my planes did), be it in B-25s, B-24s or PB4Ys...
flying and tactics are a little bit different...
of course if the AI could handle this is another question....