Leveling with full heirlooms (helm/shoulders/chest/back/pants/weapon/trinkets) with dungeon blues filling the gaps, my elemental shaman was by far the weakest caster I've played. Taking five casts to kill a generic lower-level quest mob has not been my experience on any other character in the pre-85 levels. My shadow priest in the same gear was killing everything with a single application of Shadow Word: Pain. Ditto for warlock's Corruption (and he grew up in a time before heirloom pants).
I have great sympathy for anyone who levels elemental from the start without BoA gear.