In that case i would check 2 points: in IRL fighter pilots didn't had our aiming training and they wasn't flying comfortably seated at home drinking a cola... 
Second, bombers strikes had hundred of bombers flying in formation.
And i would reply with: -
1/ Neither did real gunners
2/ Opposed by many more fighters
And add: -
Not all gunners would be firing at the same target.
Not all gunners would see the target.
Not all gunners would change the direction of fire instantly to match with one person.
Gunners were more vulnerable to enemy fire than in AH, IMO.
Gunners would not spray at a target over 1,000 yards away, as they probably had hours longer over enemy territory and had to conserve ammo.
Gunners would be afraid of shooting down friendly bombers in formation so their field of fire would be limited.
In some cases gunners had to manually swing freezing metal and bring it to bear on an enemy. They were often freezing cold, and frostbite was common.
Bombers were not rock steady weapons platforms that we have in AH.
Gunners are not effected by evasive maneuvers in AH.
I suspect that dispersion on guns in AH is off, but of course, that is just my suspicion.
Bombers never ran at full power in formation as we have in AH. The current bombers probably travel at nearly 100 mph faster than in real life. This limits the attack opportunities of fighters trying to intercept them.