Now I can add to the usual explanation, which is usually already very surprising to punters: "There could be a trainee on duty who's flustered and buggering things up. They could say 'no', even if there's not another aircraft for miles, and the supervisor will just watch it all happen."
Then your punters will never fly again if they knew the experience and competence of some of the trainee F/O's that would be receiving training on RPT jet aircraft. ATC is not different to flying in that regard. You have to let the trainee make their own decisions. The OTJI may have thought the denial of clearance was a bit harsh but would have covered that in a debrief. There was no safety issue at the time only a procedural issue. The OTJI and trainee could not have forseen what the pilot was going to do.
Are you saying, in effect, that those who happen to be flying in the system, when a trainee happens to be behind the mic, just have to wear the consequences of the trainee's lack of competence?
The trainee would have demonstrated "competence" during their training in ATC school. Those who happen to be flying in the system have to cope with the trainees's lack of experience. No one, either pilot, ATC, doctor, dentist, lawyer, engineer etc is competent to the same level as those who have been doing the job for years when they first start. To expect otherwise is ridiculous.
analyse why the instructor did not intervene at the point things started to form the shape of a pear.
It didn't go pear shaped for ATC! Once the pilot diverted OCTA the ATC responsibility was finished. According to the report the descent was at a controlled rate so I can only imagine that the pilot didn't realise that it had all gone pear shaped until the trees started to appear.
I get the frustration with ATC and controlled airspace but as LePing rightly asks, what is the difference between unable to fly a particular route because of weather and unable due to airspace? I get that in the USA pilots have a greater degree of airspace freedom but right here, right now in this country the system is different and pilots have to operate in what exists now. Rant and rave about why we have the current system but when you get airborne none of that matters, its now time to deal with the real world and all its imperfections.