JP claims
I have offered an explanation that fits all the facts, and no-one has challenged that explanation nor offered a better one.
For many of us your 'explanation' (forgive me if have misunderstood it) is that an experienced crew, not only the two pilots but also a crewman noted for expressing his views on the safe conduct of an operational flight, either deliberately or casually flew into straight into IMC and then into the Mull.
This does not 'fit the facts'. It is merely an opinion unsupported by any FR or CVR. The fact that it is similar to the opinion of Wratten and Day does not give it any particular credibility.
A system failure that prevented the intended course change and remaining in VMC, similar to other system failures which resulted in the recommendation from Boscombe Down to ground the type is at least equally likely. I prefer Sqn. Ldr. Burke's view.