7 1/4 why weak?

The old style sure grip 7 1/4's wernt too bad @ all. (the clutch Style) But as a you guys allready know there RARE & parts for the SG are even harder to find. but they are tough. (My car came with one from the factory,i also know how rare they are & how i like to drive so i sold it while it was in good working order & ponyed up for a 8 3/4) the weak link is for sure the under sized spider gears. in the open & cone style SG centers.