I find that the strength of people's ideas tends to be highly correlated with their overall skills. I don't know that you can develop the capability for good ideas without getting your hands dirty learning a field, experimenting, absorbing all kinds of information and understanding what really goes into the making of a good idea. In that way, the person with good ideas always ends up being more than just a ideas guy. They don't just have good ideas, they have good ideas and the skills to back them up. Whereas the "ideas guy" label is usually applied to people who have nothing to bring to the table other than their ideas, and wouldn't you know it, they aren't nearly as good as they think they are.
I've also worked with a lot of awful product managers. The product manager title is squishy enough that it gets assigned to people with charisma or confidence without actual skills to follow through. A bad product manager can blend in to a company for years by relaying ideas around from one group to another and having ChatGPT write documents. The engineers on the ground see the incompetence long before it becomes undeniable at the higher ranks.
When I read Hacker News and other sites I suspect a lot of engineers have only ever worked with bad PMs from the latter category.