How is it that these great barbarians leave their caves, travel thousands of miles avoiding combat dressed in loin clothes toting just a tiny ax?
Something should explain how the Wizard went from using master spells to mere firecrackers. Maybe have you play like in Final Fantasy a part where you are traveling from Caldeum to Tristram and come along some champion pack or a unique monster that wipes you out leaving you with 1hp and your memory erased or something.
This would better explain these scantily clothed "heroes to be" as heroes who met a terrible fate previously, and have to recover it. Make the Barbarian someone whose homeland was invaded; most of his kin killed and as a child, he was forced into slavery for the galley. Maybe the crew gets lost and shipwrecks near some waypoint to Tristram. Seeking vengeance, he signs up with some people seeking fame over the Falling Star rumor - you know getting fighting experience and explaining why you look the way you do.
Each character needs a unique intro story that plays like a prologue prior to even entering Tristram. Even have a unique ending where they return home to seek justice or retribution.
Heck, they did it right with Kormac. Only time will tell if he seeks retribution for what happened to him through the next expansion. Otherwise, these starting heroes make no sense. It makes sense to start at level 1, but there should be something that explains why they are level 1 and also powerful wizards or whatever in all the lore that I've read.