Oh I agree completely with your points! My thinking is that coupled with the other problems that you brought up a large cast can make the flaws and problems more apparent if the direction is already stretched thin. Movies structure and plotted well don’t have to suffer by having many character. They can strive from it. But a large cast on top of an already weak foundation can cripple a movie. Like the film had enough problems and writing a large set of characters can just kill it.