The model of the recruiting agency is that they produce a headcount you're willing to hire, and once you do it they take a finder's fee and are no longer involved.
The model of the software development agency, when you manage them correctly (which is certainly non-trivial), is they produce code which your dev lead approves of via a transparent process which you have approved of, and they have an incentive to get their contract renewed every year. This keeps them honest.
IMO when understaffed, all software companies should contract out their least essential engineering to a well-supervised dev agency rather than rush the hiring process with some dumbo external recruiter. In my experience most of these recruiting agencies have no technical people at all, can't judge the quality of a candidate, and are basically just marketing operations trying to circulate as many resumes as they can.
Maybe not exclusively, but having a strong network is one of (if not the) best ways to stay gainfully employed. The best jobs I’ve had were found through former coworkers, friends from conferences, or folks I’ve corresponded with on technical issues. Knowing and being respected by someone internal to a company typically bypasses the first two or three interview steps, insulates you from petty interviewers to a large degree, and overall greases the hiring wheels. Keeping in touch with former coworkers and cultivating friendships through conferences pays off tremendously!
I've had good experiences and bad with recruiters - the bad ones, fortunately, from the employer's side of the table, although they can't have been good for the candidates in that case either.
In the age of Google it should be relatively easy to search for job ads in a particualr area. But it isn't. Because 99.9% of the search results will be recruitment agencies.
When I search job sites for jobs within 5 miles of my home town, most of the results are actually for jobs in London, which is 30 miles away, because recruiters post ads for those jobs with the "misleading" location knowing that some people from my town will be willing to commute.
But... that's exactly the services a recruiter provides. Someone needs to make those calls if you want a new job, unless you feel that you're such a catch that you can rely exclusively on networking with former coworkers to find you new positions. Most people rely on recruiters to grease the social wheels needed to land them interviews.
I mean, it's not a glamorous profession, nor noble, nor particularly honorable. But don't indulge the conceit that recruiters are parasites. They do jobs you don't want to, so that you don't have to.