MSV ICEMAN:I think they are. Most online games I have played against the covenant are the same. The leader attacks your base at 2 min or less and regardless of what you have it is not strong enough to kill them unless the person controlling them is a complete newb. They can immediately build hunters and jackals which will walk over anything the UNSC can create until tech level 2 and lets not forget there is still the leader, who if used right is the strongest unit in the game at 2 min or 2 hours. I think if you are going to try and even the playing field you really need to make the leaders a unit which must be purchased at tech level 2. That is really the only thing that needs to happen because basic units are supposed to be the units we are fighting with in the beginning of the game. take away the immediate and free access to the one unit that can't really be stopped without heavy firepower, or slow their land speed down so that infantry can actually fight them instead of just chasing them around while they continue to destroy your base. If you are going to slow down the warthogs, which are the only thing the UNSC can use to fight cov leaders than it stands to reason you should slow down the leaders as well. Otherwise you are just telling everyone that plays this game that you intend for the covenant to be the stronger choice and the game really does deserve to have the name changed to HERO WARS
Flame turrets have been given an upgrade. You should scout early on and, if you see a leader advancing, build one or two. Flame turrets do a LOT of damage to covenant people and you can't forget that they don't have many resources at two minutes in. They can't use their powers forever. Let them drain themselves on your base while you keep it locked and build up some flamers. Just remember to make a Barracks first, or second at the latest if you expect a rush. You can usually get about five flamers and, if your opponent is REALLY slow, a couple gunner Hogs.
Covenant leader rushes are very beatable. Before the leader gets their first body upgrade, almost anything rips them apart. Afterwards they are a bit harder to kill, but usually lacking resources. You just need to practice getting some fast flamers/turrets up. Also, always scout so you know what to build counters for.
Jackals/Hunters/Grunts = flamers
Wraiths = Spartans
Banshees = Spartans/Marines.
Once they back off, build up a few Gunner hogs and send all your forces to their base and get ready for a resignation.
Game on.