I'm not sure why you would think a resto druid would have trouble healing heroics.

I have been running Warrior / Druid / 3X Shaman in heroics for a while. Druid is resto. No healing problems.

I also have no problems with AE threat generation. I am able to out-threat the druids heals with thunderclap/demo shout without issue. Obviously a paladin has better AE threat generation, but my warrior has been plenty sufficient.