Like every walk of life, there are good and not so good QFIs in the RAF. Over the years I had extensive experience instructing at every level including a spell on CFS (when it was CFS and not the neutered, scattered organisation it is now) and have seen QFIs of every ability and temperament but we did try to filter out any really bad prospects at CFS.
Fonsini, if the clip you are referring to was from the infamous Fighter Pilot programme, the instruction shown by the QFI (who I went through training with) was dreadful and I believe his instructor category was reduced because of that. The mistake the RAF made was agreeing to no vetting of the programme before it was aired