The food service is plated on Premium Rouge unlike Mainline business where it is served by courses. Premium Rouge did not have PDP but that may have been the crew. Not sure if the wine/liquor selection is different. Premium Rouge seats seem to be more uncomfortable with the struts in the way. They also feel less substantial than mainline business.
Obviously for twin aisle business its altogether different specially the lie flats.
I think in the OPs case he booked/upgraded mainline J and got Premium Rouge instead for the same number of credits. I would not be happy too.