The thing is, though, you DON'T have to chase them around, even when they are spread out - because an aware tank knows exactly where they are going. They are going toward the healer, and the healer is likely not far behind you. They all converge on the healer, then one Flash, Overpower, or Unleash and they're all back in hand again. Yes, this slows the pull slightly, but not enough to add a significant amount of risk.
A good tank will see how spread apart the upcoming monsters are, and correctly judge whether they'll be able to get them all in one aoe right off the bat, or whether they need to move toward the healer and THEN get them all in one aoe. I don't consider it to be a loss of control if the mobs are moving exactly as you expect them to, and you're responding in the correct manner to gather them efficiently - even if they smack the healer once or twice in the process.
