FCeng84 thanks for the explanation.
Not to challenge your technical understanding, but to provide and share an alternative piloting view. Concentrating on an unjammed control system in normal operation, then the basis of stick-position-control mechanism is relative to the zero force ‘in trim’ position (pilots more often relate to force than position). i.e. the aircraft is manoeuvred by moving the stick, which is referenced to, or relative to the null point, more likely zero force. The specific piloting view depends on training and / or technical understanding.
However, with either mismanaged or unwarranted non-pilot trim inputs, the reference point is changed, the zero force ‘in trim’ position does not relate to the aircraft control system being in balance (the trimmed state), thus the pilot is required to hold a compensating force, opposing trim.
Again with the assumption that pilots generally, based on overwhelming normal experience, reference the aircraft control to the zero force trim position, then all control inputs are relative to this position.
Then a failed trim condition is like flying ‘a new aircraft’, all control inputs are relative to an erroneous null position . This requires significant mental compensation of how to fly, get the feel of, and trim the aircraft - the latter being unachievable.
Furthermore if the failed trim condition also changes (AoA - MCAS) then Pilots will have further difficulty in revising their understanding. Add to which all of the consequential changes in force, feel, and speed.
Thus the apparent inability to control the aircraft (#1) involves poor understanding of aircraft control and trim interaction (172 driver #4), and similar, greater difficulties with trim failures; all of which is exacerbated by surprise and high mental workload.
A further and generally untenable view, is that pilots ‘inadvertently’ fly the aircraft with the trim - stick and trim together; yet there are examples of just that behaviour.