Wow...immediate expertise!
Big Boss...it has more to do with adjustability than anything else. The traditional setup had very little adjustment.
Turns out my car has the prototype for the first arruminum ones (additional adjustibility), but it is done in steel...came right off David K's car cuz he didn't want some lawyer suing his ass off if the first arruminum ones broke.
I'm not sure if they make adjustable steel ones like mine, so one benefit of the arruminum would be adjustibility for the handling you want. Yes, a bit lighter no doubt, but I can't imagine it affecting the P/R ratio all that much. There have been several generations, ie., the boys keep moving forward.