I find here in the valley companies value engineers who want a say in product direction. So we have companies filled with engineers who don't want to just be shoved a task and relegated to coding monkey status. I think that's where most of the ambiguity exists.
As I see it, a PM should be your team's CEO and the lead engineer should be the CTO. Together the pair of you are delivering on a single vision, one person outwardly and the other inwardly. Yet for the magic to work, the entire team needs to be on the same page. No one person should be setting the goals for everyone else. Simple put, the PM isn't the engineers bitch and engineering is the PM's bitch.
The problem is with closed-minded PMs who refuse to accept reasonable input from external stakeholders & experts. Not saying this is the rule, but it is common.
Well, to be blunt: a closed-minded PM is, by definition, a crappy PM. Listening to experts and external stakeholders is literally one of the core parts of the job.
That's not to say a PM has to take their advice. But if they choose not to, it should be for clearly defined reasons based on strong reasoning backed by data.
As I see it, a PM should be your team's CEO and the lead engineer should be the CTO. Together the pair of you are delivering on a single vision, one person outwardly and the other inwardly. Yet for the magic to work, the entire team needs to be on the same page. No one person should be setting the goals for everyone else. Simple put, the PM isn't the engineers bitch and engineering is the PM's bitch.