If you modify for zero rear toe, your next thread will be "Help, my car spins out when it turns"

Have you done the basic setup? I'm betting you haven't. Check and set camber, castor, droop, ride height, toe front and rear? That would be the 1st step before redesigning suspension components.

Trying to not be rude ...... but I can't imagine why you think you know more about car design than HPI? Do you think that they have been doing it wrong for 20+ years?