Something to consider when planning percentages is, on average, people have less experience with Axis rides since they are not usually the first choice when learning the game. Therefore, Axis is viewed as being at a disadvantage and fewer Axis people show for the frame; which leads to fewer planes for the Allies to shoot down for score. Those Axis pilots that do show either have some experience in their rides or participate in FSO with the motto "No weapon is too short for a brave man" and work to get the most out of what they have. So the Axis pilots, few as they maybe, fly cautiously while the Allied pilots, with more planes to loose, fly with overconfidence.
Overall, I would say that things worked out fairly well in that, while I too tend to think the Axis is at a disadvantage, it looks like the Axis has a chance to win. I choose to believe the CM's know what they are doing to balance the event.
<S> CMs for putting it together, and those, both Allies and Axis, who participate regardless of their rides.
MachNix