IMO shield lob is mostly to designate the priority target with out having to mark every mob. That and it helps speed up the run by having you run towards the mobs while they run to you.

SL -> Flash should give you enough enmity to hold the initial pull, and if you have any caster that manages to sneak in a hit before you even start your combo means that they started casting before you even used SL. In which case they planned on pulling early regardless of you new found lack of your protective metal discus.

Using SL at max range should give you enough time to use flash when each mob is in range, and even if they swiftcast an aoe, a flash or two is enough to get back to being garroted by baby parrots.