They are premium dlc. No kidding the French army will get a whole DLC aimed to them. Why is a Mayor player in WWI DLC....Because they are exactly a Mayor player..Would be like 'oh you want to play as USA troops in WW2 then get the DLC...
Perhaps you're right.
But it bothers me in some way.
I know it's only a videogame but some (very young) people, maybe, will see this as a historical truth. If you exit from the main campaign two main nations and make a third one the main character even if they were not a big part in it, it can be see like some kind of "cultural endoctrinement".
I don't know the game since it's not released and may be it's totally fair, but i'm a bit cautious. For example, in France, AC Unity was critiziced by some politicians for the way the game painted history (deserved or not, that's not my point here).