The thing about Resto 'Tree' Druids and Druid healing in general isn't that it can't be effective. It's more that it has had it's focus shifted towards HoT's completely. And the problem with HoT's in most situations is that they require other healers to realize this is how druids heal and play nice, because literally, with HoT's we can have our healing completely nullified by other healers tossing heals on those targets.
Lifebloom is a great healing spell. It's low on mana and with high +heal can heal for a great deal. Better yet once you plant them down you have time to heal other people or just regen. The problem of course is that 90% of that healing is at the end of the 6s in a burst. Frequently what happesn to me is the following. I see dps or other healers down -1800 or so health and not taking fast damage. So I plant Lifeblooms on them. 3s later a Paladin or Priest has planted 1500-1800 heals on them with Flashes, Prayer of Mendings, etc. So my lifebloom healed maybe 300 while it was ticking and lost that last 1600 tick that would of topped them. It drives me crazy. Because basically any other healer can make it so that I spent my mana on nothing but overheal.
Lets not forget now also that in Treeform you can't even cast Healing Touch. You have to completely rely upon your HoT's, and a cooldown ability Swiftmend to do any large amount of healing.
So the question is, what does a Full Resto Tree druid bring to the group? Easy, excellent HoT'ing capabilities. Unfortunately HoT's require 100% of your healing force to trust each other, and to be able to see HoTs are active on people. In reality that has never been the case for me.
So the remaining things a Druid would bring to the raid? Innervate, Rebirth, MotW. All of which any Druid brings to the raid as well. So you might as well bring a Feral Druid in a DPS slot for those benefits, because they won't need the Innervate for themselves, bring more Holy Paladins, Resto Shamans, and Holy Priests for the healing slots. Because until every single healer can 100% work with HoT's that poor Tree Resto Druid can potentially have their effectiveness reduced by each and every single other healer.
Edited: Edited out the Healing Touch comments since it doesn't really matter and I overlooked Gift of Nature.:P
Lifebloom is a great healing spell. It's low on mana and with high +heal can heal for a great deal. Better yet once you plant them down you have time to heal other people or just regen. The problem of course is that 90% of that healing is at the end of the 6s in a burst. Frequently what happesn to me is the following. I see dps or other healers down -1800 or so health and not taking fast damage. So I plant Lifeblooms on them. 3s later a Paladin or Priest has planted 1500-1800 heals on them with Flashes, Prayer of Mendings, etc. So my lifebloom healed maybe 300 while it was ticking and lost that last 1600 tick that would of topped them. It drives me crazy. Because basically any other healer can make it so that I spent my mana on nothing but overheal.
Lets not forget now also that in Treeform you can't even cast Healing Touch. You have to completely rely upon your HoT's, and a cooldown ability Swiftmend to do any large amount of healing.
So the question is, what does a Full Resto Tree druid bring to the group? Easy, excellent HoT'ing capabilities. Unfortunately HoT's require 100% of your healing force to trust each other, and to be able to see HoTs are active on people. In reality that has never been the case for me.
So the remaining things a Druid would bring to the raid? Innervate, Rebirth, MotW. All of which any Druid brings to the raid as well. So you might as well bring a Feral Druid in a DPS slot for those benefits, because they won't need the Innervate for themselves, bring more Holy Paladins, Resto Shamans, and Holy Priests for the healing slots. Because until every single healer can 100% work with HoT's that poor Tree Resto Druid can potentially have their effectiveness reduced by each and every single other healer.
Edited: Edited out the Healing Touch comments since it doesn't really matter and I overlooked Gift of Nature.:P