Disc oughta be fine for leveling. I dislike them as a main healer as I've viewed them as far too much micromanagement. Having to track what exact incoming damage is coming versus who has immunity, etc. was just more work than I wanted to get involved in. I also (probably due to low iLevel gear) never felt like they could keep up with incoming damage when things got exciting, whereas my druids never had that issue. All depends on what you want out of your groups. With enough iLevel, just about anything becomes faceroll.