Elemental lacks in single target dps, multi target dps when the targets are spread out, and arena pvp.
Elemental is good at grouped aoe (4-5 targets is best for the max chain lightning use)
The only reason elemental doesn't look horrible in the current raid tier, is the presence of a number of fights where the ability to use CL is so useful that it props elemental up for those fights. Combine that with a legendary meta gem that was so amped up for elemental that they can stack mastery out the wazoo and count on the meta for their haste needs, and you have a spec that looks strong in certain encounters, but it being propped up by a meta gem and an aoe spell.
Chain lightning is a different argument than the one I'd make, however it would probably be too strong IF elemental were fixed in the areas it lacks in (that most other casters don't lack in).
How to fix it:
Lava Burst scales with crit (I know, you've heard it alot, but it would help with designing shaman gear alot, and it would allow shamans to not need ridiculous haste meta gems because they wouldn't have to stack AS much haste). To account for the normal crit an elemental shaman runs with, reduce base lava burst damage 10%. This should result in minimal net increase in damage for lava burst in the gear a shaman uses now. If the shaman wants bigger bursts, they'd have to give up haste or mastery.
Flame Shock - Unlinked from earth and frost shock, no CD, acts like a normal dot. Damage increased by 300%. This would allow flame shock to function as an actual dot like every other caster class has
Lava Flows - Only procs off your most recent 1-2 flame shocks, proc rate approx equal to Frostfire bolt procs for frost mages using Nether Tempest. This would allow shamans to multidot without becoming Lava Burst chain gunners
Searing totem - Damage increased by 300%, scales with haste/crit/mastery. This button needs a better reason to keep up. Seeing double searing fireballs would be amusing and make the button important to keep up.
This combination would help shamans.....
Single Target: Slight lava burst bump, more damage from flame shock and searing totem would not overly increase shaman burst in pvp (which is good), but would improve a shaman's ability to dps without gimmicks.
Multitarget dps: Being able to multidot effectively while keeping up a single target rotation would help greatly. They'd still only have one dot, but if it hits decently, the single target rotation would work with its longer dots it could keep up.
PvP viability: They'd still be tunneled alot, but the ability to multidot, the ability to frost shock root, and the greater the threat of their instant fire spells would help them kite while using lightning bolt to bait interrupts.