I concur entirely.
However, regardless of the overall ratio determining the specific ratio by battlegroup isn’t currently possible.
Depending on how they are implemented, it may attempt to provide some balance - which would mitigate massive queues for both factions.
Or, servers will be clustered by other metrics irrespective of the ratio on the servers within the xrbg, which means we could see variation of queue based on group.
If Heartseeker, Faerlina, Grobb, and Bloodsail Buc’s are in a battlegroup then the ratio may have Ally in a large majority.
If Stal, Skeram, and Herod are in a battlegroup then the ratio may have Horde in a large majority.
My point is, there’s no way to know. The overall ratio between servers is relatively balanced based upon the only available data and server forum discussions. If there is an attempt to balance xrbg’s, then the player pool should facilitate it. If there isn’t any attempt to do so, it’s anybody’s guess what faction ratios by battlegroup will be.
That said, BGs aren’t even a concern for character migration. They will be reliant on overall ratio and how Blizzard configures xrbg’s. The principal concern is server ratio, which won’t relate to BG queues.