I do not think any other group comp beats Paladin + 4 Shamans or 5x Shamans when it comes to normal and heroic dungeon runs.

Pally + 4 Shamans is less DPS (the DPS difference between 4 Shamans and 1 is quite noticeable) but it's a lot more forgivable earlier on, once 5x Shamans get decent gear then it just doesn't matter due to everything getting killed way too fast, even in heroics. And this is all without taking into consideration min-maxing pre-raid BiS, consumables, using Drums, etc. Once you add that to either group then it's hands down better to run either, compared to other comps.