Quote Originally Posted by Fisherking View Post
When you talk of "Balance" in single player it is about a faction being strong enough to make it in the game. With all its units and so on. If someone has a very strong unit that is available late that may make up for the crappy ones it has to make do with for most of the game.

In multiplayer "Balance" is fairness. Everything needs to be a clone of the other and a unit is seen as unbalancing if it is seen to be "too strong", in other words effective.
For MP to be balanced it doesn't require every faction and unit to be identical, but it does require that they can bring an army that has an equal chance of beating any army that the opposing factions can create. If some factions are superior to others, then those factions will get considerably more use, making other factions very rare, thus robbing the game out of a lot of variation. You could even end up with only one faction being used, which would make for a rather boring game.