5 shamans is a team I want to have also, for pvp.
But I want to have a large variety of classes and I want all the other casters so going to lvl them first but really tempting to level shamans.

The aoe nuke and instant damage is so good.

Shocks non crit ~650, so ~3.5-4k damage every time shock is used, or more if lucky.
Instant chain lightning that does slightly more damage and jumps. (or instant spell to heal)
Fire Nova Totem ~450-500 damage non crit, so around 2.5k damage with 5 totems.
Goblin Sapper Charge 600 damage each so ~3k with everyone.
Ramsteins Lightning Bolts 1k damage to everything nearby.

Goblin Sapper Charge + Fire Nova Totem should almost guarantee that everything nearby dies.
1 shock or instant chain lightning should kill most people that aren't too geared.

Grounding totem doesn't break unless direct damage spells are used.

55% increased movement speed with ghost wolf with pvp boots. That is pretty nice also.

Really strong spells, easy to play and works really well to nuke with.