I think that how easy it should be to work with and direct NPCs should be directly related to a character’s intelligence stat.
High intelligence (in comparison to that NPCs intelligence) would make it easier to get them to trust you, perhaps only needing to complete one mission for them, or perhaps none at all, and they’ll simply follow you because your character passed the intelligence test against their random stat.
Low intelligence (in comparison to the NPCs intelligence) would make it more difficult to get them to trust you, needing to either lie to them, make a promise to them, or complete a number (3, 4?) missions for them, with each successful mission bringing you closer to gaining full access to their inventory, worn items, weapon choice, and general approach to enemies.