Rent seeking means taking a percentage without bringing any value. I'm on board with many of the complaints about Amazon, but it's clearly not the case to say they don't add value.

Of course many/most recruiters will also bring value, but it's a question of degree. If someone is recruiting for a technical position and they don't have the technical understanding to make any meaningful judgment of the candidate, it's reasonable to ask whether they are worth their fee. Obviously the extent to which that applies depends on the individual, the company, and the local business culture.