Well, Lightning Shield will only proc every few seconds, even if you're taking damage constantly.
That's fine, it is the mechanic of the spell.

But if an AoE caster does their AoE...
And hit only one shaman, they take 1x the Lightning Shield damage.

However, the original post is suggesting, hitting 2x or 4x Lightning Shield, is not a 2x or 4x increase in damage.
Which it should be.