Isn’t the Chazon Ish pretty much universally-acknowledged (by the Yeshivish) to have been the gadol hador? Since he said to study on Nittle Nacht, then doesn’t his da’as Torah cancel out any minhag you might have to not study then?
I can understand Lubavitchers not studying, because they (like chassidic groups in general) are very particular about following their own specific minhagim, but for general MO and Yeshivish types, why not follow the directives of the gedolim? (Actually, even Chabadniks have changed their minhagim when directed by their rebbeim; they used to wear different kinds of chassidic hats, but switched to fedoras or whatever they are now when the Rebbe said to.)