I think Skirmisher has a point about the Covvie defense though. At the moment, Playing as UNSC, I can split my fleet in two and attack from two different points at once, all the while not having to worry about a serious incursion or counterattack by the Covenant due to the fact that their fleets will be shitting themselves trying to get to their planets to defend against a massive wave of ships.
If the Covenant are supposed to defend with their fleets, buff their fleet cap so they can effectively attack and defend at the same time, or buff their starbase so that its more effective than glad wrap in a nuke blast, or give them a small amount of static defenses that are able to make a UNSC player think twice about attacking a world.
Seriously, do the asymmetric thing by all means. Its a refreshing change from most strategy games I've played. But don't leave one faction high and dry when it comes to defending itself.