I think you will find this less the case at higher levels. Resto staffs HOTs probably wont keep up with spike damage later bosses can do. Remember, these were low level dungeons. This healer had it easy: a party that never seemed to get caught in massive area damage nor failed to block full power shots. They also seemed to have individual ability to heal, or at least a potion handy. You can see some start to heal when the healer is attacking/uses no mana. Try this in a PUG and there will be wipes. However, I like the mage with resto staff combo, and previously was my first beta build before I picked another path.