Halo has 40s cd and to be meaningful requires you to be at an exact range from the boss (and btw Halo is often used to help healers, using it "because you have to move" = wasting it).
DP can't be delayed, and with SW:I as t45 (best single target choice 90% of the times) just after DP you have to stand still for 8 sec.
Instant MBs are pretty much the same as DP as SW: D, delaying them is a huge dps loss (so you can't save them).
Instant MSs are decent, but you lose SW:I to spec for them (ST dps loss) and they stack to 2 (and keeping them at 2 stacks is a dps loss).
I can't see how SPriests dps while moving is decent compared to locks who have portals, gateways and (if specced) can cast their main filler while moving.
And it's not like spriests do more dps.. locks are superior both in ST and in multidotting