I played Aw so Im tainted...but using that as an example, where the HO % was very low, only P38s really had a chance at them, I think that if they were to turn down the HO percentage you would see just how many rely on them.
When I came here I played like I did in AW, never bothering with the HO, and trying to get in position for the merge. The opponent would most always press the HO and hit me. This happened alot. If I survived, he almost always was in bad position to continue the fight, and ended up dead.
But its very easy to hit headon, and chances are you will die or be in poor shape to continue. If headon shots were lowered, all the BnZ guys as in AW, would be PO'd. Even in a 4 on 1 you could simple time his attack and put your nose to his until he passed, and quickly resume fighting the other guys.
Alot of people in here will never be geat at dogfighting, but are happy with the chance to get their guns on target anyway they can, even if it means headons. Without it, I think you may wittle down the player base to those who attend KOTH, and other dogfighting events.
The average player would find himself behind the 8-ball, and would tire of dying often and probably would quit.