The first bolded section for me is quite possible, if you are referring to atmospheric conditions in road races, though would fall under the category of "citation needed" for me. Mathieu does sometimes suffer in cold and wet, though right now not a lot of rain is forecast to fall during the race and the temperature forecast is quite mild.
As for who benefits from muddy or wet road surface conditions, especially on the cobbles, for me it is more about technical skills involved in avoiding crashes, cornering more efficiently, etc. Will Wout's pack-riding hesitancy we saw earlier in the year come back to bite him? Or is he over it? I do think, though, that launching attacks on greasy cobbles requires a good deal of technical prowess (see MVDP vs the field last year on slippery Koppenberg) and bravery/risk-taking.
In the end, though, I think under whatever conditions we have Sunday the most likely result is WVA and MVDP finishing in the lead group together and the winner in the sprint is whoever saved the most energy due to technique, team tactics, and "luck" with crashes and mechanicals.