Chug,
I also understand that the fitting of the forward HISL's on that Mk was such that pilots could be dazzled by them in such hazy conditions. Thus it is probable that neither aircraft was operating its forward HISL at the time of this accident. That would seem to constitute a "significant factor" in my book, but one which the BoI discounted by performing its own ad hoc trials and thus finding that it was not significant after all!
Without re-reading the BOI report I seem to recall that what the BOI team established was that in the conditions pertaining at the time the forward HISLs were unlikely to have been a distraction and the practice of turning off the forward HISLs was restricted to that squadron only and was not common or authorised practice across the SK fleet. Sadly in all accidents where there are no survivors and no obvious mechanical cause the BOI will always end up as an expression of opinion rather than conclusions drawn from absolute fact.
I still think you are way off the mark damning "Military Airworthiness" in the round. In most of the (accurate) cases quoted it has been chain of command interference in the process that has been the problem not the process of military airworthiness itself.