Resto Druids do bring some utility yes, but all of it is only "nice to have" and not a "must have". Compared to the encounter-trivializing spells Paladins and Disc Priests bring, it doesn't look all that appealing. As for burst healing, I'm not sure what you're referring to. All we have is Tranquility on a 3 minute timer and it is inferior at the moment to a Shaman's Healing Tide Totem.
The other problem IMO from a 10 man perspective is that a lot of fights this tier seem to be somewhat in between 2 and 3 healer requirements. It is possible to 2 heal a lot of these but also very possible to take the safer route and go with 3 healers without really struggling to meet dps checks. On such fights, we lack the raw throughput of a Monk to be an ideal candidate for a 2 healer set up, and when 3 healing, our HoTs can hardly do their job as the raid is topped up very quickly by other classes with better burst healing / or the big damage is mitigated heavily by OP Spirit Shell.