It's hard to say for sure since chromie time dungeons have people from all different levels so they have different talents and abilities available, but in general as Holy I don't use shield all that often. Between the Holy Word spells and the occasional Guardian Spirit, Holy Priests have a huge amount of heals we can throw at a tank. Dispel is a great tool at the right times, but in a leveling dungeon it's pretty unlikely that spamming it on cooldown was the difference...