Ah, menfolk. Always trying to boil down complicated interactions into one simple measurable stat. What you suggest is barely a step above letting all decisions be made by having the opponents use one of those arcade punch-o-meters, higher number is the winner.
Even if by some miracle of science you can make a sensor that can accurately figure angle and placement and suchlike to modify the force quotient, it can never factor in the element of how the other guy is prepared to receive the punch. Have you never heard the saying that the punches that knock you out are the ones you don't see? The exact same punch, down the the littlest detail, can vastly differ in damage depending on whether it's seen in enough time to let the opponent brace for impact.