desk drivers who don't agree that the PIC did a poor job
Well, this desk driver (now, but after 20K) realises the PIC may well be accused of a poor job, but the question is why. The answer to that is clearly spelled out in the report, company ethos and training being but two. If you've not had adequate training you don't know what you don't know, as Rumsfeld famously put it (known knowns, known unknowns, and unknown unknowns). If you can't get past laying it all at the PIC's door then you haven't learnt anything.
Whenever I see someone taking a whip to an individual who has erred, I always wonder what errors the whip holder has made in their life. There but for the grace of God applies to we all. You're only as good as your last flight, a NASA investigation found crews make errors on every flight, most times you get away with them, sometimes you don't.
Personally I wouldn't have a clue how to calculate a PNR or CP without getting the books out, not something that had relevance in the flying career I had.