Yet, you also used just five examples, presumably from your own experience, to tar entire professions.
Yes, there exist incompetent PMs, Architects, Team leads, and so on. There are also competent ones. Just like there are incompetent and competent engineers. No profession has a monopoly on bullshit.
The exact same thing can be said of programmers/developers; there are TONS of bad ones. The fact that there exist bad managers/pms/etc does not invalidate the need for good ones.
it doesn't matter if you have the best product in the market, if the competition releases before you and has obtained all the clients. for the client, the task of moving to a slight better solution may not cover the cost.
just because people have other jobs, it does not make them stupid. of course, what i've said in here is over simplified, there are a lot of other jobs required in order to have a healthy, viable product with clients and cash flow.