How is there even such a thing as a "pure healer"? I think you mean to say "a healer who spends 70% of the time doing nothing", because unless your group is intentionally screwing up you're never going to have to heal 100% of the time. I don't care what the content is, you're always going to have some downtime. What on earth else are you going to do while waiting for someone to need healing if not DPSing?