Also i found the Earth Mimbari war in Babylon5 crapful for the same reason. The fact that Mimbari ships are invunerable to Terran weapons except when their great leader is on board is most idiotic!! And why couldn't Terrans learn from the Japaneese of WW2 and use suicide nuke runs to destroy Mimbari ships?? again, prooving it is a stupid story.
Actually, you're missing a lot of the story with that war. When the ship with the leader was on board in the attack that caused the war, their defenses were down. They didn't have up any ECM, shields, etc. Pretty much, they were coming in with defenses down and gunports open to show that they were friendly and to give the humans the respect due to warriors. Having gunports open like that is incredibly dangerous, since any targetting computer worth its processors will be able to destroy your guns in the first salvo, leaving your only options to be running away or dying.
After that, the issue is ECM. With the Mimbari ECM up, human targetting sensors couldn't lock onto their ships. In effect, the humans were firing blind. Their automated defenses could do nothing more than randomfire, which made them just as much a danger to their own ships as to the enemy. Plus, I'm willing to bet they couldn't bring the bigger weapons to bear, since I bet those would be slaved to the targetting computer. And without the bigger cannons, they were at even more of a disadvantage.
I'm willing to bet that humans actually did destroy several Mimbari ships during that war. However, they had to do it using risky and often suicidal tactics. Tactics that they couldn't afford, since they'd need every ship they could get ahold of to last as long as possible. Also, I'm willing to bet they didn't know the exact size of the Mimbari military, thus making it impossible for suicide runs to be a viable strategy. What good it is to suicide bomb if all you do is end up opening the front door for the military?
Basically, humanity was outgunned, outnumbered, and forced to play defensive. No matter how you look at it, they were in a situation that was a tactical nightmare.
One question: What is Dawn of War?
It's a video game adaption of Warhammer 40k (which, in turn, is arguably the source of StarCraft).