You can’t violence your way into efficient human labor without repealing the 13th Amendment.
Let’s see if the SCOTUS says that the slavery clause only applies to individual people that congress specifically designates as free, a la the wholly made up rules on the insurrection clause of the 14th amendment.
I’d make the argument that slavery provides a higher quantity of workers, but since it’s against the workers’ wills, it is not as efficient (units of work per unit of time).