To me, the role seems to be like 95% charisma as it's largely a figurehead position. Foreign relations, domestic relations, commander in chief of the armed forces are all mostly charismatic functions.

The smart but uncharismatic folks seem better suited to institutional roles where they can guide policy in the right direction without being the public face of the policy. It's not all that different from the distinction between sales and the folks that design/make the product; the groups are complementary but divergent.