I think this would be a good change. Right now, many long rounds end up as friendly fist-fights to the finish where there's a lot of players fighting just one or two. There's a disincentive though for archers to turn and fight because they have no chance against melee-strength opponents in a fist fight. If punch strength were determined by only a character's strength, and not powerstrike as well, then more archers would turn and fight.
This is a small change that will have a small effect. It's main purpose is to give archers more incentive to turn and fight at the end of a round (or throwers to, as sometimes happens). It's not a balancing change because it's not actually affecting balance very much. It's main aim to to change incentives just a little bit.
I don't mind end of round boxing. It's a fun way to end very unbalanced rounds and is a nice change of pace sometimes.