Vipper showed the real stats. Atm in the monthly breakdown there is a disparity of 6,5% between winrate of OKW and highest allied faction in winrate. The difference to lowest allied fation in winrate is 11,4%. At games with Players above Top200 the disparity rises to 11,7% (best allied faction) to 13,4% (worst allied faction).
I personally think it should be okay if OKW perfomces somehow worse in teamgames than in live.
The only difficulty is to hit the right spots, you have to weaken mechanisms that are strong in teamgames without influencing 1vs1 stats which are a lot closer to beeing balanced.
In addition to that, the stats clearly show that OKW is the most played faction (in addition to the highest win rate).