World of Warcraft Death Knight, Death Coil mistake?

The dice pool on Death Coil is strange to me, the pool being based off of Cha mod and also capped on single use by Cha mod than coming back on a long rest seems likes an oversight or mistake.

I think the dice pool should be Death Knight Level + 1. 

You mean something similar to Level 3: Healing Light (Celestial Patron)?

Maybe it's simply for balance reasons due to the damage die?

I guess another option could be to set a fixed number depending on your level, like Level 3: Warrior of the Gods (Path of the Zealot)