Didn't read the complete thread, but there was some discussion a while back. Changing it to increased accuracy to the target and a small penetration boost was the outcome of that as well as reliably having vision on it until the plane gets shot down, if I recall correctly.
+ %dmg messes with the damage numbers on units and makes it easier to oneshot vehicles, as well as synergizing too well with other offmaps.
+ %accuracy alone has too little impact on the heavies, like KT / JT / Tiger, as those usually get hit anyways. It still helps to a degree for flanking / circling them as you fire on the move.
+ %pen alone would have too good of a synergy with the USF AT (cause it stacks with their abilities) and the ISU.
Other possibilities include:
+ Boost ROF against that target
+ Increase chance of crits