From playing some more as a resto shaman with a marks hunter friend I have to say that indeed a focus macro and proper interrupt on a pally is the only chance we really have against a warrior/pally combo. The hunter can do a pretty sick amount of damage, and can use silence shot and scatter so we can usually make the pally bubble if I can interrupt correctly. It's still very touchy and nearly impossible against a good team though. A well geared warrior can sometimes put out so much damage that with MS I cannot afford to use a GCD to interrupt, or sometimes the pally stuns me (if they kill the grounding totem), or bubble then get into melee range of hunter etc. It is however extremely satisfying when we pull it off
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Overall I'm rather happy playing as resto shaman in pvp even in 2vs2 - we're not that great but we do have our strong points. The biggest difference in how well you do at least to me has been using focus macros effectively or not. Many caster teams can really destroy us if I don't use ES well. The biggest problem we find as well is me getting cced. Still with proper use of LOS/shock/grounding totem (and of course tremor and poison cleansing against those ccs, hopefully the other team doesn't kill them) you can keep yourself out of ccs for a decent amount of time - hopefully enough for your partner to kill one of them.
Of course if they had changed our trinket to remove CCs, that would have helped alot.