You could always do 5 druids and still have the holy trinity (I've been thinking a lot about doing this lately).

Alternately, just doing 3xdps going with warlocks isn't too bad -- they have SoC that is easy to aoe with. I haven't ever used rain of fire on them.
Druids have a non-targeted aoe once they're leveled up as well.

I don't really see how you can go too wrong with any of the ranged dps classes -- sure you may not be able to use the mage's targetable aoe's, but you've still got a few options (including blast wave and arcane explosion). You'd be happy with any of them, really.

Only problem with that second team is they will all be using the same gear (except the tank ;p)
Doesn't the first team have the exact same problem?