I never said they were always needed. I'm simply saying that if you're either: in a PUG that isn't as efficient as a prime LS group of 6, or if you're in an LS group where more than 6 of you want to go, that taking a SMN along isn't a bad option at all.
You may not 'need' to slowga all the mobs that link to the NM, then run off and dismiss the avatar to de-pop them, but it can save you a couple of minutes per NM. If your group isn't perfect, then that might be the difference between a win or loss.