I change my opinion to this. 1. He is the GOD of war. (literally) 2. If he dies war stops. 3. He has killed other gods.
He is pretty hard to kill. So far I'm I think at 3/4 of GoW2 and I haven't played GoW3 but he has been "killed" two times already buy he just climbed back up from the Underworld.
After becoming the God of War he took his Spartan army and started conquering Greece. The only reason he was stopped was because Zeus first tried to crush him with the Colossus of Rhodes but that failed so he just stabbed him with a sword that absorbed all his powers.
Not because of him being a bad leader. In fact, Zeus "killed" him because he was becoming to powerful.
I don't think that's possible if the leader of the gods is actively trying to stop you. But Kratos also was a good Spartan general before he became Ares' servant and ultimately he led an army of Titans against the Olympians and basically kills all of them (except for Aphrodite, he screws her).
Aeneas. Then again, he wasn't competing with the leader of the gods (just his jealous wife, if I'm not mistaken), and his mother (another goddess) helped him out, but still.
I'm telling you, the greatest military leader is my alternate universe doppelgänger; Lion El'Johnson!