That it takes your exotic slot? I'm using an elemental primary for end-game content anyway, and either a shotgun or Black Hammer. Yeah, I'd use Gjallerhorn before SGA, but SGA can get the job done. It's hardly a wasted spot. I'll give you downing Crota should only be done by rockets, but in every other situation that you can abuse the perk, SGA is just as viable. I'm not really sure what mines you're talking about, but if you mean the ones you destroy in PoE, a primary can take it out as fast as necessary.