That is also MY beef with CAM. I'm not in favor of STP, but I am in favor of allowing more tire in STU for the entire class (if they can fit it under their fenders) and/or more tire for solid-axle cars AND more suspension allowances for solid-axle cars like rear relocation brackets.
Instead, now anytime someone says they would like more Ponycar allowances in ST/SP they are being told to just go run in CAM. So the pressure to make the late model Mustangs and other modern-ish stick axle cars competitive is off. And if they aren't going to be competitive, serious competitors will not prep them for the class. And if they aren't prepped and run, then there is no basis for the SCCA to make allowances for them to level the playing field. It's a Catch-22.