Heroes have really helped me out a lot. I remember I struggled with lots of missions but ever since I learned the right ways to use the AI, I've done much better. I even recently got Protector of Cantha, which I'm very happy about!
Never underestimate the power of the hero/henchmen AI. A perfect example would be in one of the Nightfall missions where you have to kill the harbingers with holy water. Well, the PUG group I joined was good, we took care of all the margonites including the mobs around the bonus harbingers but...there was some confusion as to where we should all go. For some strange reason we split up and the NPC we were supposed to protect died.
With heroes and henchmen, you have a great, great advantage. One mind is controlling the action instead of multiple people trying to sync together. Pulling is easier, group actions can be more polished and I generally prefer henchmen over people in most cases.
They have their limitations but that seems to take the backseat when my interrupter ranger makes sure Glint never casts a single skill or when Olias helps to make Varesh as annoying as a hangnail instead of a major headache.
The one seriously major gripe I have about the AI is the lack of a command to have someone pick up an item! My primary character is a warrior (secondary is a dervish) and it's very annoying to carry staves and urns around.
Oh well.