Everyone other than the zerg factions of various PvP servers are tired of constant zerging while the other 2 factions just lack in numbers.
Idk about other platforms but on PC EU the zerging is bad and no matter how good and skillful you are you simply don't take down 30 people soul assaulting you at the same time... and that's only one example.
Solution:
Add a queue above 2 population bars. Leave the queue on until all 3 factions have 2 bars, then you can move on to 3 bars, queue until all 3 factions get 3 bars, then move to full.
I don't think you have to kick people out if let's say AD goes from 3 bars to 2 (which will never happen XD) from the other 2 factions, but at least don't let their numbers increase to full population until the other factions are AT LEAST close to that as well.
This wouldn't only sort out the lag a lot when the servers aren't full, but also bring balance to PvP numbers-wise. I can't really think of any cons to this.
So... PLEASE.