Wow, that is the most thorough and complete accident report I think I've ever seen! My admiration to the team who investigated and created that report!
It seems possible that the pilot mishandled the plane to the point of spinning it. I've spun a Grand Caravan a number of times during formal flight testing. The plane will enter and recover in accordance with the requirements, though the spin is more extreme than a pilot might have come to be used to flying spin approved Cessnas. The spin looks like this:
The airplane with forward C of G takes a very nose down attitude (as much as 80 degrees, I saw), and must be allowed to accelerate before being pulled out of the dive. My recoveries were generally approaching Vne, and more than 2G (I had equipped the test plane with a G meter). As the Caravan POH states, ailerons should not be used during spin recovery, as the corresponding roll spoiler also goes up, and delays the recovery. Spin recovery is rudder only.
Engine torque, as noted, can also delay spin recovery. The first action in the POH for spin recovery is power to idle. I have done flight test spins in other types where the entry was required at 75% power, and the result was often a snap roll, rather than descending spin.
Last December I was flight testing another Grand Caravan. Though Transport Canada Flight Test Branch [of Aircraft Certification] did not require me to deliberately enter spins for this testing, they did require a demonstration of spin resistance with the modification. I was required to take the plane to the point of stall break, entering with 30 degree angle of bank, 75% power, and one ball out (which I found was pretty much full pedal application) - both to the left and to the right. The plane handled these aggravated stall entries very well, and though dropping a wing, and going around a little, recovered right away when recovery control inputs were made. Altitude loss was minimal.
The Caravan is excellently designed to be spin resistant, and I have validated this during several flight test programs for modification installed on them. I also flew jumpers for years (C 185 & 206) and understand the desire to get the plane back on the ground quickly - sometimes for cost, other times just for pilot glory/entertainment. Sadly, and plane can be pushed too far. Combined with too low, and we all know what happens.
If I were still involved with jump operations, this report would move to the forefront of pilot training material for me!