Aside from the fact that this discussion is pointless anyway because you won't convince any relevant people to add more units to the game (and for good reason), why do you want to balance the play rates at low level anyway?
Paying attention to low play rates for faction generally makes sense, because it could be that nobody picks them, because they are weak. We have already established that they are not at high level and it seems that you argue that even at low levels they are not percieved as too weak but rather too much effort to play.
So why is that a problem? If one factions playstyle appeals to a rather small set of players, why do we need to change that? I really don't see the issue. To me this seems like trying to get the play rates up for the sake of "this is how things should be" while it is very plausible that you wouldn't solve this problem by making changes to the unit roster at all, as FtX pointed out.