I don't necessarily disagree, which is why I think GMs want managers who are going to be open to the FO's suggestions. Yes, there are certainly going to be times when a GM dictates some things to the manager. For instance, a GM might want a certain player to get more playing time, for one reason or another, than a manager wants to give him. But I don't think that GMs really want to interfere with the day to day decisions like line up construction and bullpen usage.
Along the same line of what you are saying, and I know you disagree, but I think that's a big reason why LaRussa was hired. Dombrowski gets credit for trying to embrace analytics with the hiring of Cora and the special liaison guy, but he has his old school guy in place as an advisor, 'just in case'.