Actually disc is good imho with improved Penance through 2/4 T18, and with enough luck/good positioning one may have lucky 4/4 T18 strikes too. In terms of healing, as a disc I have healing on par with our shamans and often with our druid. (who is slightly above us) We also introduced a holy priest to our roster, but we haven't yet made enough tests to see how she's going to fare inside.