The problem is that Bungie wants to do both of those things. That is, they'll put in a spongy boss/mini-boss in a room with barely any cover (if there's cover at all) while also throwing hordes of infinitely-spawning adds at you. Toss on explosion damage from the boss hitting you behind what little cover there might be and you've got a recipe for a miserable experience. Bungie just does not understand encounter design or balance. At all.