I can't speak for the others, but my tactics are based on shock and awe military doctrine, which calls for usage of overwhelming firepower and displays of force, in particular with an intent to terrify and demoralize. It doesn't matter if it's inefficient. That's entirely the point. It's intended to give the impression of being readily and easily capable of utterly, brutally, and ruthlessly savaging each and every opponent at provocation. Of giving the impression of being someone to be feared above and being the kind of destruction even Blasters like Purity and Legend could unleash given provocation.
But then, I'm a former military man, and I think a lot of us former military people get overwhelming firepower lodged in our heads at some point. In this instance, I believe it's a valid tactic against a trio like the Dragonslayers. Also, I've been entertaining the notion of deliberately recording the ambush, and if it goes to plan, using the footage to build reputation for future incidents that call for ruthlessness and overwhelming firepower.