So, you're saying the tanks aren't the leader. You are, clearly! What if the healer is new and can't deal with a full pull? What if the tank is a beginner with questionable gear and is more comfortable with a single pull? This isn't the end of the world if the tank is single pulling, it's way more toxic if you're a dps for exapmple and is pulling ahead of the tank. You're imposing your gameplay style on them. What if because of this the healer suddenly can't keep up with the heals, or the tank doesn't know how to deal with that many mobs for whatever reason?