In pve priests were barely above the other classes in healing and will now likely be last. The problem was the mana cost of penance and PoM not the healing it does, every healer should be able to do that level of healing, it just shouldnt cost 79 and 58 mana respectively.
You brought priests not because priest was OP but because priest met the MINIMUM requirement for a healer in phase 1, the other classes besides druid dont meet the MINIMUM requirement.
Shamans, paladins, and mages dont meet the MINIMUM requirement at level 25.
No healer will meet the MINIMUM requirement at level 40 because of MS.