The Aircraft was hand flown from a stable configuration into a stall situation, albeit unwittingly complicated by the autotrim..... leaving the best aviation experience/resource in the non control role , or absent from the cockpit and not decisively involved throughout.
The problem was a skill, perceptual (including spatial disorientation) and CRM one on the pilot/company side, worsened by design faults with the aircraft ( pitots, autotrim, stall warning parameters useless in a mjaor attitude upset, no A of A display, digital readouts vs analogue readouts worsening performance in emergency environment, unobserved sidestick)
Mimpe, pretty well covers it....