I don't think all PMs have easy jobs or are useless, and I even know PMs who I think have kind of easy/unimportant jobs (not that I would ever tell them that about their job) who still take a lot of pride in their work and do work hard anyway. But I do think there are lots of PMs out there who essentially fill the role of "business analyst" who end up doing low-skill things that fall outside of easily-defined role-buckets. That's not the employee's fault so much as the organization's.