First of all, if the Allied squads had attendance that averaged the higher side of their commitment numbers, like the Axis squads did, then the 55/45 split would have been held. Not the Axis' fault if you guys can't show up.
Second, the Stukas were still wiped out before the target.
Third, the overall attrition rate was very close on both sides. No side ever had manpower advantage over 6 at any time I checked the players in flight.
This tells me that a 50/50 split would have been better for balance.