I know CH isn't an especially realistic game but I thought I'd mention this anyway. Actual Warhammers don't have massive heads, they're more like your average nail hammer but on a longer shaft as it would be ridiculously unwieldy otherwise. A maul is a hammer with a large wooden head, thus about the same weight as a much smaller hammerhead, but its a tool and not particularly good for fighting as it just has a lump of wood at the end thought often seen in fantasy (Thor though its magical and he's a god so we might have to let that one slide).
Most of this can also be said for axes, though they didn't make ones with wooden heads. I think it would be really cool if CH got some more realistic weapons along with maybe some balancing to make them all useable.