By chance can you post photos of the failed tires showing the wear?

If one assumes on a new 600 or 550 there is no mechanical failure, the photo link is a severe alignment problem not air pressure related. If over inflation eliminates the inside edge wear, pay plenty of attention to center tread wear.

For passenger car rear tires, inside edge wear is from to much toe out......i.e. the car is dragging the rears on the tire's inside edge. That is why the outside edge shows no wear.

Caster is a front adjustment that addresses steering control etc. No rear tire/suspension application for a passenger car. Performance cars are another matter. Camber, for a passenger car, is pretty much a front adjustment also....not the rears.

Esentially, the rears are along for the ride and the front does all the work, hence all the adjustment capabilities to the front.

Admittedly I am not familiar with the 600 suspension. However, my 550 only has toe adjustment on the rears. I am assuming the 600 is the same.

Unfortunately, I have experienced bad alignment from a dealer only to be corrected by an Indy. I suggest you find an alignment shop, not a tire shop, that has an excellent reputation and established track record that knows MB suspension. It's not rocket science. My high school job was in a shop that specialized in alignment.

BTW, my only S550 tire failure was like yours. Inside edge right rear. That was in 2013 and none since then. My TP stays at 36-38 psi. No over inflation.

Good luck. I wish you the best and hope you don't have some imbedded hidden mechanical failure.

Here is the data sheet from the dealer alignment on my S65. There is a way to adjust Toe of the rear wheels.