Find the AOPA synopsis of his flight. I was a member at the time and read it and I was almost sick to my stomach. No I am not instrument rated, but you get the sense he got spatially disorientated and didn't believe his instruments and went with the seat of his pants feel. The tell was the rapid speed increase before impact. IMHO that is I don't know up from down and pulled back on the stick when his was in a deep left hand spiral if my memory is correct. He was probably almost inverted in a dive.
Any of this other conspiracy drivel is an insult to all of us who lost friends while PIC and have read their NTSB reports. These accidents are always a seris of bad decisions that end up in a less than optimal outcome, unless is is an exogenous event, aka engine failure, control system failure or structural failure, the last being very rare.
He could have asked his instructor to come that day, or decided not to go, or called a Maday or let a tower know he was need of flight assistance because he was temporary disoriented. Boston or Fall River would have given their eye teeth to help him if they knew it was him IMHO...
You summed it up very well. From the radar images, it appears that disorientation was the issue. Someone who knows more about it than I do said a very rapid shift to autopilot would have been the best hope. It could quickly have levelled off and stabilized the plane. Even that would have required extremely fast reactions, though. They say the average lifespan of a pilot after disorientation sets in is 178 seconds. Not long at all.
‘Meanwhile, the flight path of the Saratoga is getting ever more erratic.
21:39 The aircraft entered a left turn (towards the east) and climbed to 2,600 feet. As it continued in the turn the aircraft began a descent. Soon, the aircraft was descending at 900 feet per minute.
The aircraft stopped turning, flying east now, but continued to descend at 900 feet per minute.
20:40:15 Still descending, the aircraft entered a right turn. As the turn rate increased, the descent rate and the airspeed also increased.
At the end, the aircraft was descending faster than 4,700 feet per minute.
A reason for this may be that the aircraft was upside-down in a downwards spiral and that the pilot tried to pull back, thus accelerating the descent. He would have done this simply because he no longer had [any] idea which way was up.
21:40:34 The last radar contact with the aircraft showed it at 1,100 feet.’
https://fearoflanding.com/accidents/accident-reports/which-way-is-up-john-f-kennedy-jr-plane-crash/