The fourth character would be intelligence-based because you need 2 physical damage dealers and 2 magic damage dealers to be balanced in terms of actual gameplay - not a theoretical, "on paper only" concept of balance.
The game has about 34 Talents and you can have 5 Talents each, so 20 Talents. There are 7 Civil Abilities and you have points to max one. There are 17 Combat Abilities and you get the points to max out two. But not all Talents and Abilities are balanced with each other or are worth taking. Again - that's actual balance, not theoretical.
Physical damage dealers want maximum Warfare on both - not just one. The probably-ideal Civil Skill balance is Persuasion, Loremaster, Thievery, Lucky Charm.
