I'm one of those "healers that only heal" but I do so for a very good reason: I am piss poor at dodging, a problem exacerbated by lag. When I played SMN (taking a break from healing), I would die at least once a dungeon once I hit HW because I couldn't stop my rotation and get out of the way in time. SMN was fun, and I was even good at it, but to quote a tank I met in DF 'You do good damage, you just need to dodge more.' The latter simply wasn't happening, and I came to the conclusion that playing SMN simply wouldn't be viable for me in the endgame.

Do I have downtime where I stand around and do nothing when just healing? Yes. But that downtime often equals the precious second or two I need to get the hell out of the way of an incoming AoE.