Hmm, think of it like this, if you are a hardcore PVP player then you will choose the race/faction (and in sod/era even class) with the best PVP options. This leaves the other faction with more casual or unskilled players which creates an imbalance. This imbalance then leads even the casual or unskilled players to migrate towards the dominant faction en-mass just so they can share in the spoils. I know people that rolled horde even though they are not super PVP players just because they wanted to be on the winning side.
If this imbalance would also bring a cost for these players then they might be willing to switch sides and help bring balance, I’m not saying it will be 50/50 but even 60/40 would be close enough.