I can't blame him for that, as my main is a shadow priest. Shadow is a lot of fun, but it just isn't very strong in pvp. The only DoT we have that does a significant amount of initial damage is DP, and it costs quite a bit of mana and we can only have it on one target at a time. Mind Spike does a pitiful amount of damage really (at least by itself) and Mind Blast has an 8 second CD which makes spamming it kind of hard.
Disc has shields, atonement, and with Holy Fire and Smite they can put out a decent amount of damage. I leveled as Disc until the 50's, and it's a lot of fun too. Tell him he should try it. If he doesn't like it, fine but he should at least give it a shot.
____________________________
Guild Wars 2, Crystal Desert server:
Inga Freyasdottir, lvl 40 Norn Mesmer
Deathbringer Kaami, lvl 16 Asura Necromancer
Popina, lvl 15 Asura Elementalist
Althaia Willowbark, lvl 7 Sylvari Engineer
Maeve Amnell, lvl 4 Human Guardian
The MMO-Zam's FB group. Please message me first so I know who you are.