Surely the THS MUST respond to SS elevator demand? There can be no other function for it. The problem is that no-one KNEW that it had. This is either a basic lack of knowledge of the a/c or a total blank-out of understanding in a crisis, and I do not know which.
Way back (after PGF) I suggested that surely there must be a THS angle, (AB, or Boeing - viz AMS) beyond which one should not normally stray, and that a mandatory 'Over-ride' function should be required before the THS is permitted to move past this limit, which has the effect of alerting the crew to what is happening and yet giving them the option of doing it if they feel it necessary.
Strong nose-up THS forces have caused or threatened too many accidents.