I'd suspect that all the lane maps (White Ball, Red Ball, Hamburg and to some extend Arnhem) being the most popular maps have quite a significant impact on the Allies/Axis global win ratio because those maps are relatively easier for the Axis with their HMG 42s and especially superheavy TDs, and because most casuals have a hard time dealing with them. Sadly top 200 3v3 and 4v4 data is such a small sample size that it's unreliable, but at least in 2v2 with a bit bigger sample size it shows that within the top 200 the Axis/Allies WR is mostly fine at 52/53 vs 49 (with the exception of UKF, but again that could be skewed due to low sample size). I'd consider anything between 47-53 to be good enough.
Also the Allied factions seem to rely more heavily on light vehicle play, as indicated by high WRs in 1v1 for USF and SOV (but not UKF who lack an AI LV), which makes them very good at 1v1, but less so at teamgames where LV play is weaker.
UKF is not doing well, but that's why they are getting a boat load of buffs to their doctrinal arsenal in the upcoming patch. Along with a heavy nerf to Jaeger Armor.
I wish we could add the Land Mattress and the Calliope to the stock rosters of UKF and USF, as I reckon that would improve their performance (mostly on the lane maps) dramatically, but sadly that's not going to happen.
Error margin is can be an argument if it doesn't shows always the same factions on top and always the same faction on the bottom, if we were seeing Allied bottom one month and then Allied top the next month you're analysis would be correct but we're far from it. When there is always the same factions on top and the same on the bottom that's not anymore error margin, that's inbalance.
Then you're just explain us that water's wet and you can't do anything about it.
Finally you're telling us oh sadly Calliope can't be stock this didn't stop you to decided to nerf to the ground Scott and Pakhowi which were the lower version equivalent of Calliope for USF. Oh and after those nerf USF players are picking even more Calliope so now its time to nerf it too, too bad.