I have noticed that some hirelings are working wonderfully while others are working erratic (standing around doing nothing). Seems to do a lot with the kind of commands that are available. For example, I have observed that FvS hirelings with Holy Smite command are a lot more aggressive and effective in CC, while higher level FvS hireling without Holy Smite never cast this spell and tend to be a lot less effective overall.
Likewise Clerics carrying only Heal and no moderate cures can tend to wait until too late to throw you a heal, while lower level Clerics without Heal patch you up more readily.
It is frustrating when a lower level cheaper hireling consistently outperforms the higher level counterparts. Can we perhaps customize the commands/spells available to our hirelings?