I think we can all say the current implementation of hirelings and their ai is a bit on the lacking side. They make decent bots to stand around on levers, maybe heal you, buff you somewhat, etc. But when it comes to contributing to doing a quest, they lack the insight into adventuring that they need.
I really think hirelings should have scripts to follow. You have a handful of archtypes to use, so making a barbarian and a fighter would or could use the same script. Instead of having the hirelings a contractual purchase with timers, they should be in the quest panel at the door. Or at the wilderness entrance. You check off the class you want, it has an associated cost in plat, and when you enter, they join.
These NPC's shoul be capable, but should not be capable enough to complete the quest without the players help.
This would allow utility npc's to provide more assistance than they currently do, and offer ways to boost the capabilities of the npc's so they provide a wider range of options in a quest (more than 3 or 4 spells).