It depends on the pull and your party members, really. If the group is doing one pull at a time, Eos CAN solo heal an expert dungeon. If your tank and DPS are using cooldowns effectively, even big pulls become trivial with Eos. I once had the tree + two bees pulled into the group of Vanu and the totems; a Whispering Dawn under Fey Illumination, Convalescence, Mantra and Rouse is nothing to scoff at. Of course, in DF, you can get anything from really good members to just horrible, horrible people.
So really, it depends on the group. I've had some terrible, TERRIBLE tanks that I could barely go into Cleric Stance for fear of my paper-thin tank tearing, but on the other hand, I've also had groups where all I do as a WHM or AST is Divine Seal/Synastry -> HoTs -> burst out the Holies and Gravities.