From the evidence it is clear that this accident was not caused by mechanical leadscrew problems. As soon as the AoA reaches about 20 degrees the PITCHTRIM moves down at a very constant speed, exactly following the described MCAS operation. This is consistently dealth with by the PF through regular TRIMUPMANUAL inputs after which the down trimming halts for a few seconds (the way MCAS has been stated to do). At the end these TRIMUPMANUAL inputs are of shorter duration resulting in a runaway down trim.
The PF was continuously up-trimming as required until those last trim inputs. Those were too short, perhaps because of other distractions. Although the crew was aware of the continuous need to apply up-trim they apparently did not use the auto trim cutout switches.