Except, as melee, when you step back, you are not dealing damage, thus lowering your DPS and making archers more desirable.

As for curing yourself - either you are using TP abilities to do so (thus lowering your DPS) or being an MP sponge. You won't have enough mp yourself for more than a couple cures (unless you're going to disengage, lowering your DPS) and more people needing to be healed means that you need more healers (or your whole group has to go slower and wait for MP if you don't all just wipe).