No argument here. They could even make a few spawns and call them Lesser Behemoths or Juvenile Behemoth or something, to reflect the fact that their loot wouldn't be nearly as good as their elders. As you suggested, merely crystals and a handful of other things. It's nice that they've taken steps to eliminate MPK'ing and kill-stealing by having more NMs and HNMs force spawned and locked to those whom made it appear, but at the same time it removes a bit of ambience from the world as well.