I agree about product owners. I have never seen one that could really guide a project from start to finish. They either don’t understand the tech sufficiently, or they don’t understand the business case or they aren’t engaged enough.
While they may not be common, actual product managers do exist. There are a lot of incompetent ones, to be sure, but there are also a number of incompetent engineers.
It’s so nice to deal with experienced product managers and project managers but it’s rare to deal with them.
Where do all these PMs get promoted to? If it is to a "manager of PMs" role, that sounds as if the company is always launching ever more products, and that promotion to a higher level with more pay while remaining a PM isn't an option.