You're not accounting for the fact that climate control systems use recirculated air. The a/c system is not cooling outside air 50+ degrees, it is recirulating interior air and cooling it via multiple passes over the evaporator. Eventually the discharge air reaches 50 or more degrees below ambient, but the intake air at that point is well below ambient as well. The MB climate control manuals give detailed information on the parameters used to select fresh vs. reciruclated air, and in the case of the 124, whether to use 80% or 100% recirculated air.

Agreed that 70 degree discharge would never cut it in 100 degree weather. BTDT, as a matter of fact.

My 30 degree observation is not an opinion, it's based on empirical data I gathered over the course of ownership of my 124.193. During which time I replaced the evaporator, all vacuum actuators, the condensor, the compressor, the manifold assembly, and ran it on 3 different refrigerants, collecting data all the way through.

On my 123, I designed a modification to take it from the factory maximum of 80% recirculated air to 100%. On a 100+ degree humid day, this change resulted in a 5 degree drop in discharge temperatures, taking it from approximately 55 degrees to 50 degrees. I do have a little bit of experience in this area...