The Crimson Binome
Hero
No matter how awesome he is - level 20, straight twenties across the board, max roll for every hit die - he would always be better if he was using a more effective weapon. That he doesn't do everything in his power to minimize our chance of death (barring unreasonable resource expenditure) means that he's not taking this seriously, and can't be trusted.Of course you're ignoring the possibility that the guy with the mace is badass enough to not need a bigger weapon.
It's not the actual in-game effect of using the objectively inferior weapon, as much as it is the thought process which would cause someone to make that decision. There are plenty of reasons to use a mace instead of a warhammer - proficiency, magical enhancement, availability - and this person just needs to give one good reason to justify making this decision.
Wanting to look cool is not a good enough reason to justify the increased risk of death. Neither is superstition, or heritage, or anything like that. Those are all meaningless in the face of an uncaring world.