Bombers will almost always outnumber turrets, therefore an average of 3 attacks per bomber. The current average against a T2 target is 1.67, so even your modified system would be nearly twice as powerful as at present.
I suggested a similar system to this a while ago, but the numbers were 1 attack if less than turrets, 2 attacks if more than, with fighters counting double for the purposes of determining outnumbering.