The stupidest cope is that Sukuna is nerfed because "he doesn't have 20 fingers"
By his own admition, Sukuna's mummy made up for the missing finger. To make up for something means that there is no loss, the end result is the same level of power.
Which means Sukuna's mummy = last finger
The only valid question, which we do not have the answer for, is whether the last finger still has any CE/power within it. Or is it void now that the mummy was consumed.