Kit d'Rection KG - there are several points here. The accident was caused by something that happened on the runway, not after leaving it. Only the FDR (and CVR) will determine this. Any witness marks will only show the position of various controls at impact and not where they were before touchdown and during the landing roll - agreed? What happened to the controls between the a/c leaving the paved surface and impacting the building is of little relevance. Who knows what inputs were made in those appalling few seconds? Hence the use of the words "relatively little value" and "Only where there is no FDR reading of throttle position on the runway will witness marks etc be relevant." which you no doubt saw - and it obviously is with reference to the throttle lever positions.
The intention was not to address professional accident investigators (like you?) but to try and dissuade the others from pointing out the full left rudder deflection on the remnants of the fin etc, and now where the lever was (possibly?).
I agree that accident investigation is not for 'pilots' per se, but I actually do have experience of such (No FDR). What are your qualifications, and do you have any useful input on the results so far?
Regarding the 'mod' bit, the intention at all times is to try and keep the thread focussed, and threads like these easily run away as I can see from the number of posts here deleted by the seniors.