The trigger works, but as has been said, you need to let your healers know what's going on. The buff that causes the shield to trigger lasts a long time (I believe ~24 seconds? I'll have to double check this evening). But the intended use case is to use it a substantial amount of time before a predictable period of heavy damage. For example, I usually pop it just before the last of Waukkeon's ads dies, to shield for when he does his AoE knockback. It's also useful before Nidhogg casts his ultimate. I usually pop it just before the last dragon dies, which gives the healer plenty of time to activate it on the group when we're stacked.
It is a very situational attack, but for those situations, it is incredibly helpful. A 1500HP shield can really soften some harder-hitting boss fights.
I will agree, though, that the range needs to be increased. Right now, it only covers melee, or if everyone's stacked.
EDIT: Here's the macro I use:
/macroicon "Divine Veil" action
/action "Divine Veil" <me>
/p Cast Divine Veil! Heal me to activate a shield for everyone nearby!