I severely doubt the racials are the only things driving the win / loss rates. I doubt they'd made that much of a difference at all really.
You can't just blanket win / loss statistics, you'd need to analyze everything:
Race, class, spec, food buffs, flasks... and of course, skill level... which could "kind of" be measured by what % of players possess certain achievements (On a whole most people earn curve / cutting edge / rating / gladiator, etc, not buy them for real or in game money) and their performance on logs, what % of these people do arena, at what rating etc.
There could be so many contributing factors that I doubt changing the racials would make any difference at all. Maybe horde players use more foodbuffs? Maybe more gnomes use flasks in Alterac Valley? Maybe the Stables is too close to the alliance gate in Arathi basin? Maybe the warsong hold is more challenging to assault?
The racials seems a very specific and niche factor. You'd also have to scrutinize a whole lot of other factors to even come close to decent data suggesting something as minor as a racial ability is a determining factor.