First. Would you please offer another Rishon besides the Rambam? Not that I disagree with you per se, but even the Rambam was cholek on a lot of his shitos regarding these inyonim. Regardless, I think you meant to say “hold like” not “believe” since even the divrei chol of the Rishonim are Torah.
Second. “Artscroll must have quoted from a sefer” So it is easy to believe that Artscroll got it from somewhere but not easy to believe that this sefer got it from Rav Chaim?
Third. “but he is MECHUYAV to do so, <stong>if he learns a sugya differently.” Did you do that?
Lastly. While I strongly suspect that Rav Chaim has opened a SA a few times over his life this is not my problem. My problem is for those that want to bring a proof from their own svoros like “that can’t be true” or the like.