On top of this, I just want to mention: The skill gap in healers isn't narrow at all. Stroll on over to FF logs and you'll see it's very, very wide. The different between, say, a 99 percentile healer, a 75 percentile, and a 25th percentile healer is enormous - far, far bigger than the same differences between tanks.
And for extra fun - it's wider than DPS most* of the time too, even if you don't adjust for DPS classes' much higher damage ceiling. I don't think it's unfair to say that, overall, healers have the largest skillgap in the game.
*with 2 exceptions, black mage and red mage, that are comparable to healers' skill gap.
