Except a large part of the OP was about someone _informally_ taking on a _specialist job_, even though it's not specially in their job description, and then getting penalized for it career-wise.
It was a specialist job. It apparently wasn't one anyone else was doing. It was a job that someone(s) _did_ have to do to make the work go right.
Shouldn't someone have that, indeed, specialist job, and do it? Whether you call them a "project manager" (that's got "manager" in it), a "scrum master", or some other kind of "manager" -- why are these crucial _coordination_ tasks being left to whatever developer happens to step up to do them, at cost to their career?
I've always thought it was the manager's job to do things like, especially, "updating the roadmap, talking to the [stakeholders], noticing the things that got dropped, asking questions on design documents, and making sure that everyone's going roughly in the same direction."
Many of those things can be categorized as either removing barriers to implementers getting work done, or making sure the implementers are getting the right work done. Isn't that what (various kinds, including "project") managers are for? Indeed it is a specialist job.
If they aren't doing that -- what are they doing?