Enhance shamans HAVE to be paired with DK(s). They absolutely HAVE to be.

1) You can rely on DK HB spam to keep people snared. If you run frost weapon on at least one guy, unleash elements will reduce their movement to 70%.
2) Shamans have limited root breaking and while they can put out a decent bit of DPS at range with shocks+unleash elements, grip solves a major problem for them.

I'd say those are the two main reasons why 2 DK's + 2 or 3 enhance shamans is going to work better than just enhance shamans.