In your step, you are assuming that the maximum value of static friction is asking, but that is not the case. Static friction can have variable values, with a limit that it canot cross. When a solid cylinder is rolling down, lesser frictional force acts on it than if a hollow cylinder is rolling down.

In your step, you are assuming that the maximum value of static friction is acting, but that is not the case. Static friction can have variable values, with a limit that it canot cross. When a solid cylinder is rolling down, lesser frictional force acts on it than if a hollow cylinder is rolling down, while you have assumed it to be the same for both cases.