That factions physically have units in their roster that enable them to compete effectively online doesn't mean they're any weaker or stronger in SP. The strength of factions for SP is much more determined by their starting positions and economic issues. It doesn't matter if a faction has powerful units if they're not able to afford to maintain them or tech to them. This is kinda where I see the single player balance and challenge.

People seem to be missing the point though, for MP differences between factions are good, otherwise why bother having them, but factions still need to be able to be competitive and to have more than one option so as to not be predictable. This has nothing to do with starting areas, surrounded by enemies with a poor economy.