Get the WowCensus addon and check it for yourself. Create a character on both sides and run a census.
You probably won’t believe my stats but a couple of weeks back Earthshaker was 57% Horde and a bunch of ES Alliance were complaining that more Horde guilds had moved in since then. Then the big Flamelash Alliance exodus happened, plus a few Horde guilds from Flamelash too. Given the existing population ES won’t be above 55% Alliance; it’d need be a pretty insane swing to go from 57-60% Horde down to less than 45% Horde.