STS is, like mentioned, active only briefly after TO - it is not active at any other stage other than if the SMYD detects an approach to the stall, in which case the STS trims nose down at the same time as the Elevator Feel Shift Module adds pressure to increase control column loading, in combination behaving like an old fashioned stick pusher to make the effort on the column to pull the ac into a stall at least twice what is needed without the systems fighting the pilot (at least, that what the NG does, and I think the Classic was similar, though it has been a decade since I last flew one). So, a malfunction in that system could have been an issue, but the FDR reportedly suggests no malfunction.
Equally, a runaway stabiliser would cause a big pitch moment if not responded to in time, but wouldn't cause a full deflection column input.
I had misunderstood the information regarding the incorrect positioning of the AC - I had thought it was vertical profile and hadn't realised they were so far out laterally too. Quite astonishing that anyone would try to intercept an ILS in IMC at 1000" and so close in. Have they never heard of MORA/MSA?