Baston,
Is your memory so bad you have forgotten that all this has been discussed before.
Everyone accepts that the lighthouse observers were in fog. Most people accept that Mr Holbrook describes (marginal ) VMC.
Since the Chinook crew were neither in the boat or the lighthouse nobody knows if and when the Chinook went IMC.
Now most of us accept that because of the close proximity of the crash site and the lighthouse,it is highly likely the crew went IMC. That does not constitute absolute proof. Remember the discussion on well defined fog bank edges? There were no observers at the crash site.
Even if the crew went IMC, to be negligent it would have to be deliberate and with the aircraft under control. Sqn Ldr Burke, the leading expert of the time, says this "may" not have been the case.