Often presented as fact, Vette's theory about mindset/false horizon causing the pilots to 'see' a flat vista of ice stretching out into the distance is nothing more than an idea
How very wrong!
Sector whiteout is well known and well understood.
Mahon saw it for himself during a 212 flight along the final approach profile of the fatal flight. It was even videoed.
With sector whiteout, which can occur even when the nominal visibility is a hundred miles or more, is a pernicious phenomenon and is so common in that part of the world that it may not even be correct to call it a phenomenon at all.
Fast forward to 38:10 in this video to see a description: