You have to be in melee to use it, and you're in melee with no shield.I think the warlord with his maul and Dwarven Weapon Training just wind up being a powerhouse combo. What exactly is the trade-off for the maul's exceptional damage anyway?
But regarding the discrepancy, the big difference I think is that there is a ton of feats & now items for weapon users, and barely anything for the wizard & warlock (& devoted cleric). Which makes it strange (to me) why AV has such amazing out-of-the-gate power creep with the new weapons and why the first splat is for weapon users. Perhaps as 3e had some big mage-lovers on its design staff, 4e's designers have swung the other way...