I'm playing a Crusader, currently level 21 with the bottom half of the support tree filled out. I rely on turrets, but I've noticed they are very dumb and don't always engage nearby enemies. Sometimes their slow turning speed is to blame, but other times they simply don't target enemies.
As an aside, it seems odd that their health doesn't scale with my level. Currently they are glass cannons for me, so I have to be very careful with their deployment so they don't get one-shotted.