The whole RNAV thing is a c0ckup because the lateral navigation performance figures were based on the old inertial nav, using which a 747 pilot might know his position within a few miles. Today, with GPS, the whole required nav performance thingy is moot because you could fly, in a spamcan, from here to Mongolia and then fly back with the two tracks within not many metres of each other
Today's INS (in modern jets) is also accurate enough (with DME or GPS fixups) for any practical purpose.
But it seemingly has not stopped a whole load of committees jumping on the RNP boat and drawing up loads of "standards" which are irrelevant to actual flying and just cause certification nightmares.
PRNAV could be extra nasty because ATC will potentially be able to instantly verify whether the airframe on their radar has PRNAV approval. They can't do this for BRNAV which is taken on trust. So anybody flying a PRNAV procedure might be taking on a bit of a risk, one day.