Ok - while I would agree that disc priests aren't required for LK-10 normal I can't really agree with this. There are good reasons to be disc in LK-10 if you have the spec.
- Easier Infests - even if only a bit easier than pre-Hotting & a PoH
- Easier Mana management - LK is a long fight, discs longevity helps it
- Stronger single target heals - important in quite a few phases
The big advantage of going holy in LK-10 is B&S. So it comes down to this - if your dps are failing on defile - go holy, otherwise disc has the edge. If you're holy and don't have B&S specced - then respec or go disc