The use for Rusch's ratio is"how important is it for biologists to study this particular payoff structure"? Your suggested revised ratio wouldn't be good for that.
It might be good for something else - rationality training? But that's a different subject. I suspect that, even in that context, the PD is overemphasized, and other structures relatively neglected.
Is it important for biologists to study the payoff structures like 'stab yourself in the eye' or 'get into a fight you can't win'?
Hannes Rusch argues that the Prisoner's Dilemma is best understood as merely one game of very many:
http://www2.units.it/etica/2013_2/RUSCH.pdf