I don't think that is quite how it works. In any case, in battle you are not just making more units but are actively recruiting local manpower into your army. The implications are not.... pleasent.
You are essentially racing your opponent to conscript as many men near the war zone as possible, tearing them away from their families to force them to fight in your army after a crash training course in whatever mech, tank, or vessel you need them to pilot. Then of course you could well have them fighting their friends, neighbors and even brothers who would have been recruited by the opposing side...
However, the units you start out with on the Board Map merely represent the units you will pop into battle with. Like those mercenaries you could hire in Starcraft II: Wings of Liberty. They allow you to get a foothold and start the match off with a few advantages. A particularly large force might even be able to end the battle quickly but I doubt that.
How they manage everything after that? I have no idea.
