I dislike the idea that “wizards can do this at level 5, but martials doing it ever sounds kinda OP.” I chose 8d6 for a very deliberate reason.
8d6 at will, 8d6 3/longrest, and 8d6 1/short rest are 2 different things.
The 1st is Tier 3 11th level power for any class. The 2nd and 3rd is Tier 2 5th level power for any class.
Now Rogue is an at will class, it gets the 1st one at level 11.
if Wizard is a long rest class, it gets the 2nd one at level 5.
If Fight is hybrid at-will and short rest class, it either gets the 1st one at level 11 and/or the 3rd one at level 5.