Indeed it would totally amaze me if a UK FTO pushed its piston fleet through PRNAV approval, at a cost of perhaps £5k-10k per aircraft, for the paperwork (totally irrelevant for any IR training purposes, anywhere in Europe AFAICT) but a zero functional improvement.
The paperwork cost was in this case quite low, because the approval was sought in conjunction with GPS approach approval. It was a single mod at the time. From memory, it was nothing like as high as the costs you mention.
"Dangerous" assumes operational relevance, no?
No it just assumes that money, concentration and time spent on pointless certification could be spent on something that makes a genuine difference to safety instead.