A20 out-turn some fighters with full bomb load, without any structural damage done to it.
No it can't. I've flown the A-20 a fair amount in dogfights, and I don't think it can outturn fighters even when the A-20 isn't carrying any bombs. If you think so, I suspect that you are looking at an unfair comparison, like situations where the A-20 has more E that it is dumping into temporary turn rate, and you are mistaking that for a situation where both planes have the same E.
The turn capability of the A-20 isn't horrible, and is great for a bomber, but it isn't in the same league as fighters.
Also, it's all about g's. An A-20 can certainly turn when carrying bombs. If that turn generates less than about 3-4 g's, then it's fine, as the airframe with bombs loaded can certainly handle some g's -- just not 6 g's with bombs.