Well Charm does have Perks for Governor, and it does raise relations. So in a sense it's probably one of the best skills for a Governor.
I don't think Steward as a skill alone has any appreciable effect on the Fief. i.e. It's not like a high Steward skill increases taxes anything. It's just running a Town/Castle grants Steward XP.
Perks/Culture is what it all comes down to for good Governance. Unless someone has proof otherwise? The Clan panel there should show the highest skill an NPC has really, rather than any one fixed skill.