Saying it’s often some new grad is like saying there’s no point having an on shore dev team because the devs are often fresh out of university. If you continually hire terribly you’re going to have a bad result.
A PM should become the subject matter expert in the product they are developing. They should be able to field questions on most every part of it, and be able to build a roadmap of features. Communicate with all teams associated with it. Having the programmers plan all features is a recipe for disaster if your product isn’t designed for developers. It’s like saying you don’t need a qa team because the developers tested it.