It's not just that. Arguably it's easier to get top 100 alliance as they rarely fill the 100 before it's closed.
It's the gravitation that having so many really good guilds has had on the player base, I'm not there because I want top 100, but I do want to seriously try to clear each mythic befor the next raid release. Which comes with alot of leg work, and that's just a hell of alot easier in the faction where most of the people wanting to do that harder content have congregated.
We know hord and alliance pop wise are actualy 50/50ish, yet there's massively more hord guilds logging mythic kills and clearing heroic and sich faster, more m+ players pushing in the 10-20 brackets, there simply more people doing the content I most enjoy so naturally that just then makes it easier to do that activity.