Well of course it's not ONLY them - you doing assist dps on full kidney shots etc helps with a lot of kills.
But the faster you are on the important things, landing the right fears after cyclones, assist dps at the right times etc, the better your team will do - believe me a good priest can carry a lot of the faceroll of most WOTLK burst classes.
RMP is my favorite comp - you get to really play everything - defensive, offensive and dispelbot.
RMP is also where the priest can shine, you get a chance to really win or lose the match at various points - and the diversity and extreme CC of a RMP is insane when put together properly. I would go try it if you are bored with your current setup - definatly. Watch some movies, Hydra is ofc a good priest to watch, but his gameplay is not as offensive as some other priests - you should watch a lot on Warcraftmovies.com - just find all RMP movies about 4.50 rating and learn away
Peeling is simply when you get in trouble - if you get raped by 2 shadowmourne melee with a droolcup, peeling them off you means the rogue and feral druid going on them, slowing them, stunning them, cycloning and generally stopping them from killing you.

Peeling is important in a setup where your only real cc requires the druid to make himself vulnerable - if your partners can't peel, you will not succeed with that setup
