XxjimandjimxX:three star units are basically immune to counters. i had a game once where all i built for 8 minutes were 3 flamers and 3 rpg marines. by the time they were 3 stars, they had killed 3 rebel bases and 20+ jackals, and fended off a RAGING ARBITER twice.

How?  Their strength is only double. Halve the time it takes Jackals to kill a regular Flamer and that's how long it takes to take out the improved one.  You'd also have to repeatedly use up heal and repairs on the group.  If you challenge them with a small force, you are just asking to feed them though.

XxjimandjimxX:mabey you could make it an upgrade in the temple, requiring the tech upgrade AND possibly a very expensive veterancy covenant

As stated before, it takes a long time to for them to recoup the costs of the upgrade, in addition to missing out on a leader.

whitemage:you will never be able to counter attack or expand... all he has to do is take map control and stop you.  a mono arbiter will rage anything you build...

[1 Star Vet/Defense Gauntlet] Jackals deal 150 DPS vs. Covie Leaders, hell, [1 Star Vet/Peon] Grunts deal 97 DPS vs. Covie Leaders, and something tells me they will cost more for the Arby to rage than they do to build while they're at it.

Put simply, they have more supplies and better units.  1 Star Jackals vs. Hooks will equal easily secured Hooks and 2/3 Star Jackals, which in turn equal dead Arby.  Good luck taking out a Hook with a 2/3 Star Grunt or Jackal on it.

whitemage:marching slow army around the map would be slow and agonizing.

Ghosts and Banshees aren't slow.  I'd still probably allow Covie units to teleport from Grav Lift to Grav Lift, something they can almost do anyways.

whitemage:covenant is built around the leader. most of thier units are worthless without leader support.

Which is why they are all toughened up.  They deal more damage per second, and they survive for more seconds, it adds up rather quickly.

whitemage:you cannot launch an attack with this, all you can do is defend.

launching any attack would mean your base will die because locust or something will be droped in.

The only thing that can get back to base anyways is the leader, and I love it when my opponent saves me the trouble of having to kill their leader and army at the same time.

SMART covenant players build shields.

whitemage:unsc only work because they have hogs and pelican.

Huh.  I never use the former beyond early crate collection, and use the latter extremely rarely.  Good to know that I didn't use a workable build getting up in the top 50 a while back, and repeating the process currently with the same.

Pelicans and Recall will not save your ass from an invading army, its much more efficient to use them offensively than defensively anyways.  Its much simpler to make sure that your attacking army is a bigger threat.

This will occur easily if you have Shields and commit any reasonable amount of anti-building DPS to your forces.  By the time they can even touch your buildings, you've already wrecked half of theirs