I think the better comparison is the nova bomb. The hammer does explosive damage vs. single target (ignoring the combustion perk if you are standing next to someone who gets hit). You can hide around a corner and shotty camp a gunslinger for a trade at least, but you can spam hammers at a corner and kill everything around it without even getting into shotty range. There is absolutely no advantage in any way a nova bomb has over a hammer, while a hammer has a crazy number of advantages over a nova bomb.