Imagine a three corner room:
In one corner, you have the proactive healing types (mainly disc)- that while they are good, just seem to have no real synergy with the reactive types. Okay, we understand the whole "sucking up the damage" thing, but it also shouldn't be to the point in which other healers cannot compete on fights other than burst damage (in which disc can be weak on).
In the other corner, you have your reactive healing types (holy priest, resto shaman etc) that are the "I see damage, I heal it" types.They have no absorb type mechanics (except pallies)- all of their healing is based off of how much damage people are taking. Put them in a group with an absorb class, it just doesn't work out as hot.
In the third corner, we have the HoT classes (druids mainly). They're great for spread damage.
There has got to be a way to synergize these three to actually work with each others benefits and weaknesses.
The problem reactive healers are having mainly has to do with absorbs. If I get into a group on this one that has 2 disc's and a holy pally, there is no way I'm going to ever be able to compete. Now you add a druid into the mix, he/she is throwing out his/her HoT's while I'm still in the middle of casting my second heal.
By the time that heal goes out, I might as well have not thrown out that heal because that person has already been healed.
So, what am I good for? As a reactive healer, it almost makes me useless. Resto shaman aren't the only ones in that boat. Look at holy priests. Big advantage holy has over resto shaman: more AoE heals one of which they can actually use on the run.
So, tell me: where's the synergy? There really isn't any.