It still ends up being Blizzard’s fault for their design choices. Letting free xfers for smaller factions is what killed Stalagg, Flamelash, Skeram, Heartseeker- the choice to do that instead of faction specific queues from the start is 100% Blizzard’s fault, and completely to blame for the massive difference on those servers.
You can’t blame players that jumped ship, many of them did so not because of what the server was like at the time- but what they feared it would become (and what it did become) in phase 2.
Now- just think of who is left on Flamelash, the most extreme- there’s multiple peak hour videos up with /who 60 that hits 15 players. Imagine at peak hours there being 15 level 60s on the entire Alliance- you can’t do anything with that.
The problem is- look at the benefits and penalties for each faction:
Overpopulated faction benefits- can farm/level with ease in peace, no competition for valuable mats, can reach any dungeon without effort, still get benefit of xserver BGs.
Penalties- none.
Underpopulated faction benefits- none
Penalties- can’t do anything in the world without being camped until they log off or reach an instance portal to escape.
Now, there’s a lot Blizz can’t do without taking away player agency, however there was one thing they can do, and it was something they DID do for 90% of Vanilla. Same server BGs.
Will one incentive to be on the lower pop side swing the balance? No, of course not- but it would not only help, if it was known from the start it may have changed player’s initial choices.
Why would Horde move to HS if they still have long queues? Why wouldn’t Alliance move to HS knowing they’ll have instant queues?
If there’s zero penalties and all the benefits for stacking a server, of course it’ll happen- and it did happen, and it won’t fix itself. Same server BGs is quite literally the last chance Blizz has to at least attempt to fix this problem- don’t get me wrong, I can’t see them doing it as they clearly want there to be horrible balance on servers so they can sell lots of paid xfers later on- but if they want to at least try something to save balance, that’s it, cuz after BGs are out there’s nothing left.