The tire pressure recommended by the TT maker is the value needed to carry the load. Often it is also the max tire pressure.
Depending on the load, my D rated tires can be varies between 55 and 65 psi. Many folks just run the max pressure and be done with it.
Biased, radial and diagonal plied tires have all been around for decades. TT makers choose the type that will do the job for the TTs intended use. Hence many folk choose to upgrade their tires.
Of course the majority of the TTs and 5ver have their original tires, when their owners trade them in.
Safe travels