My experiences with PMs were universally good; these are people who would look at ideas in-the-baking and find ways to improve them, run interference for a number of projects, put together decision-guiding research, and generally somehow manage to bring things together.

There are bad apples in every bunch. The reason MSFT has so many PMs is not that they are under-competent; I suspect it has a lot more to do with the fact that it is a large organization that is often unable to silo teams from each other effectively.