I disagree somewhat. At least, in my experience:
Experience 1: 25 years old and applying for a $200k/year job. I didn't get it :( but the recruiter had my back and significant sway with the employer. He filled around 10 roles per year. He was also buddy of the person I sat next to but this was unknown to me, I was cold-called for the role. "This is small-fry for me, I usually just fill $500k+ roles."
Experience 2: Recently (10 years later) a recruiter asked me my expectation "It's in your interest to get me as much as possible" was my response. I _know_ there's more to a job than financial package, but that was that question dealt with. She called me after each interview within the hour, and gave me status updates every 2 days over a period of 4 weeks. Happened to be in the same city on a trip, and had lunch together. Nice lady. Didn't take the role in the end. Still in contact, no bridges burned.
I also agree somewhat.
Experience 3: I sit next to an HR Ops team that staff large tech companies. A team of 20 people that download and forward CVs all day. The level of technical questioning before forwarding a CV is "How is your XXX language" and that's that. Applicants are sorted and pigeon holed into buckets depending on existing role and package, and no more. They have no bargaining power with a client (on either side) as they simply don't understand anything related to the role. Their KPI is how many roles filled, that's all, and when the client gets unhappy they email the GM.
So, in my opinion, it's mixed. But some headhunters really are good. Differentiate yourself, make yourself special, then the good headhunters will seek you out.