I've got a kinetic/energy brute. Probably my first toon to get fully T4'd with incarnates. Although KM is considered weak among melee sets, it is still perfectly functional. If concept is king, I think you'll find KM/Energy to be a fun combo.
Necro/poison may be another story, however. My experience with poison on non-MMs is pretty good, but I don't have much experience with it on MMs.
The biggest difference (other than debuff strength) is MMs get Noxious Gas, as opposed to Venomous Gas. NG gets cast on a pet, has a long recharge, and none of the debuff is enhanceable. VG is a pbaoe toggle where the to hit and defense rebuffs are enhanceable.
NG really needs some love.