I believe you're right. As far as caster dps goes, having a Boomkin, Shaman, and Mage together give more synergy.

The boomkin will give +5% spell damage, and +3% spell haste.
The shaman gives spell power, mana regen, and spell haste, plus elemental oath for increased crit for all casters on occasion.
The mage buffs the shaman with +3% spell crit, which in turn helps on the elemental oath.

A pally tank adds great synergy with mana regen, and gaining from the spell damage buffs, as would most healer classes (perhaps a pally healer the most due to the crit buffs?).

I'm close to this with my group, but I love my hunter too much to drop her, and like the rolling hots on the druid as well, though this one is less important for the way I spam spells.