Most powerful duo?

[Tecmos Deception]

Realistically, shaman+enchanter have no detrimental overlap.

Yes yes, they both can slow and charisma buff and root and do a few of the same debuffs. But these overlaps are good things, not bad things.

It is a good thing that the shaman is the main slower (better slow, better able to handle aggro after a resist). It is a good thing that you have two people to try to slow very resistant targets. It is a good thing to have stacking MR debuffs for pets and very resistant targets. It is a good thing to have more charisma on the chanter. It is a good thing to have two classes who can root instead of just one.

The only overlap that isn't good isn't bad either, because the debuff spells like cripple don't get used anyways.

[Elements]

Depending on the specific targets you want to do it will end up being bp cleric + warrior or enchanter+cleric/shaman