As long as absorb heals and spread out fights exist, shaman healing mastery will never be good.
Those that say otherwise don't truly understand resto shaman.
I played a Resto Shaman for two years, right through Firelands. I think I understand the class just fine.
Absorbs are less of a problem than you think they are. They're the most visible problem, but it seems like a lot of people are ignoring the underlying problem ALLOWING them to become so prominent (that would be mana). There are a couple of things that could be fixed that would greatly help Resto Shaman, but nerfing other classes isn't going to fix them. Resto Shaman wouldn't be doing any more well on spread fights, or rapid movement fights, whether you have a Disc Priest or you don't. I raid tested as a Shaman last weekend, and I didn't have a Priest anywhere near me most of the time. The problem was the movement and the spread. It wasn't the Priest. I still looked like absolute crap on the meters because I was constantly dodging...crap.
1) Shaman need something for spread. And "something" isn't a 2.5 second cast spell on another 2 sec CD. I'm sorry, but it doesn't cut it for most of these fights.
2) Shaman need something for movement. Something that they can use more often than every 2 minutes, and no, HST doesn't work for this.
3) Shaman need their Mastery retuned. Blizzard has given healers, as a whole, far too much mana this expansion. Shaman shine when healthbars are low. Healthbars will never be low unless other healers are unable to keep up, which only happens when a) damage is intense enough to punch past their throughput cap and b) they don't have enough mana to keep spamming their highest HPS heal. So for Shaman Mastery to "shine" in this environment, they need to tune it up so that it kicks in at a higher level of health.
Or, alternatively, they can nerf the crap out of mana regen, but I really don't see that one happening.