There are exceptions. For example, A New Leaf, was on its way to a ponderous three hours with results we will never see it seems, but certainly became a sharp and charming comedy in its released form, probably a brilliant save on Evan's part, although it did not do well at the box office anyway. I would certainly like to see the director's cut on this one.
The director's vision should accommodate reality to some extent,for example, it is simply arrogance and bad faith on Von Stroheim's part to "envision" a movie that requires a nine hour run time, as was the case in Greed (1924). Do we condemn the studio management for objecting to the sheer cost of producing so much excess movie. If the director has no interest in producing a movie with some semblance of commercial reality or an understanding in advance to fight some good fight or other (e.g. Paths of Glory, a deal made in advance in exchange for work in The Vikings apparently with the idea that the latter would surely make money, and the former only fine reviews) he should be funded by backers interested in art at all costs not a commercial studio. All the same it is a shame so much of it was lost when Thalberg took the axe to it, the damage having been done.
Another exception is Cinema Paradiso that is thought by most to be a masterpiece in its second, shorter form and less good in its original longer form.
For Being Human there probably box office problems either way so it would have been better to die with the boots on, and run time longer.
Good Times, Noodle Salad