Mine didn't. I always felt that properly geared (and not necessarily über-geared) they were way to powerful.
I must have been doing something wrong... because after I'd played through the game a few times I'd make characters in solo with a good amount of magic find and as much gold as I wanted and load my merc up on equipment and it'd still die to almost any boss/miniboss/unique mob of monsters.
I still think ranger is a good idea, traps, bow, and... some other tree... don't think we really need a melee skill tree... I mean let them dual wield like swords and such just don't give them skills to do with it.