The problem with Lava Burst as our main dps tool in Wrath, is for it to auto-crit we need to preface it with Flame Shock.

The healer will know that you are bursting target "X" because they have a flame shock per shaman burning on them.
When lightning was the default attack, it hit as hard with or without other spells already on the target.

In previous seasons of arena/pvp, we could have a macro which would "/cast [target=focus] Big Nuke" and another for "/castsequence [target=focus] Nature's Swiftness, Big Nuke, Earth Shock" or whatever the rotation was.
The healers would be watching your toon target another toon, and not even see the damage coming.
So the annoying <insert class> would be made your focus, and then not targeted as you did dps on another toon, saving the big nukes and cooldowns for when they stood in the open.
And when they see you throwing volley after volley at the warrior, with all of your toons targeting the warrior, they would feel they were safe to come out and cast <insert annoying effect>.
At which point, you'd quickly burst them down, via a [target=focus] macro, and they'd be dead before the healer could react.

Now, we have the choice of hidden focus target, with Lava Burst that is not guaranteed to crit, followed by other spells with cast times and/or Earth Shock.
We do not have Nature's Swiftness in the best Elemental builds. Non-crit Lava Burst (granted some of them might crit) is not optimal, when you can have an auto crit via Flame Shock.
But if you Flame Shock the <insert annoying class> and then start to burn the warrior, its fairly obvious the focus target might be burnt down.
If they have a pally/disc priest on their team, not only can they dispel the Flame Shocks (magic based) but they could bubble/pain suppression the Flame Shocked target, as they see your toons casting Lava Burst.

The best I can see is... focus your true target, and then have Flame Shock working on them and another target, so the healer does not know where your burst will be.
Or, burst your focus without a Flame Shock opener, and hope the not-guaranteed-to-crit spells will add up to enough burst damage to kill it.