Even though my title, salary, and perks were still the same, it was a de-facto demotion. Important parts of my compensation (involvement, agency, sense of ownership, diversity in work effort) were just inadvertently phased out as the company I helped grow was big enough to support product managers who could do just the most rewarding parts of my job but not actually code or anything.
I think (hope) there are things that one can do to guard against this from happening, and just being aware of this phenomenon is valuable.