I think he's probably perfectly fine at planning and executing self-limited military campaigns, and he doesn't waste men (as you say of Travis/Servalan) nor forget an army marches on its stomach. But as to government or a long-drawn out military campaign, I think he does as his Steward tells him. It's the unquestioning loyalty that buys him Denethor's love.

ETA: I'd buy he was a good judge of character, perhaps, which is a decent transferable skill.