Ah, Discipline Priests. According to some meters, they are the worst healers. According to other meters, they are the best healers because their shields prevent so much damage. What's the truth? Who really knows? Probably somewhere in the middle, would be my guess.
All of this is because the combat log does not report absorbs correctly.
The lesson here is, again, one of feedback. You need to feedback to be able to correctly evaluate abilities.
How does Sacred Shield compare to the other abilities? Is it weak or strong? I have no idea. I take it on faith that it's doing good, so I keep it up on the tanks always. But I really don't know.
That could actually be another point in favor of the FoL paladin healing style. Focusing on Spellpower gives you a really strong Sacred Shield. Maybe that's the element which makes the build truly viable. We don't know, though. We can theorycraft, but theorycraft really needs data to confirm the math.
If you have a game with a combat log, all effects need to reported and properly attributable. Blizzard really needs to get a proper reporting system for absorbs up and running.