I'd also mention that Doma and Gyr abania certainly look bad but those are two provinces, both of which have little to offer, especially Gyr abania. Natrually they gave access to new warrior castes to bolster their army but other than that they likely saw little profit to be made and as a result were treated worse. Obviously this isn't a good thing but the point is that there would be provinces that are treated fairly, I'd also imagine it's largely to do with the actual legion governing it which most legions would have their own ingrained culture depending on the upper command, in the 12ths case it was more or less violence and magitek experimentation. So we haven't seen that much of garlemald yet and should they prove to be dastardly evil at every turn than it's rather unbelievable that it could function as a superpower at all.