Well.. How is that any different from a Titan or Warlock's first choice in the same situation to spam their sticky grenades as well. The only difference is that those grenades--the Fusion and others like it--are glorified bodyseekers, and will kill an enemy even if not thrown on target. With a tripmine, you actually had to hit the enemy straight on, with little/no aim assist as a factor. If you stuck the enemy, it's because your aim was true, not because you threw a grenade in the enemy's general direction. And even after all this, you still stood the risk of killing yourself with your own grenade, something very much lacking by the other classes.