> If they're good at whatever it is they end up doing, that's good.

As a former PM (now an engineer), I think that's pretty much it. Teams and companies will vary a lot in terms of what they want the PM's to do, with some common patterns emerging, but as long as the PM's do the work well then the team is much better off. The key issue is how much you can trust the PM to hold up their end of the project.

A common theme I've noticed among good PM's: good judgement. When the team can trust the PM's judgement, the whole team flows better. When the team can't trust the PM's judgement, the PM is worth negative bandwidth.