You still get drops from yellow named mobs, just not exp/sp. So it has nothing to do with mat farming. They implemented this tactic to prevent astral/aoe burning. But basically because the mobs have a fairly small stray zone before they return back, they implemented a system that was not needed, and basically made aoeing useless outside of a few mobs in behest and leves. Just remove aoe attacks if you are that worried about someone killing 3 mobs at a time...