What one recruiter actually gives you
A recruiter is a person with relationships. Those relationships are real and they are valuable, and they are also finite. They know the people they have placed, the people who have applied to them before, and the people they have met in the specific corner of the market they happen to work in.
On an ordinary search that is enough, because an ordinary search has plenty of qualified people and the job is mostly to find the ones who are open. On a hard search it is not enough, because the qualified population is small and the odds that it overlaps with one person’s address book are poor.
The failure is quiet. You do not get told the network ran out. You get a slow trickle of candidates who are almost right, and a series of updates explaining that the market is tight.
What actually makes a search hard
Three things, usually, and often all three at once. The skill set is narrow, so the qualified population is small before you filter for anything else. The location is specific, because the work happens at a site and cannot be done from anywhere. And the people who can do it are employed, doing it, and not looking.
A controls engineer who has commissioned the platform you run, within driving distance of your plant, who is open to moving, is not a person you find by searching harder. It is a person you find by knowing where that kind of engineer congregates, which is a different thing entirely.
What changes with several specialists
Put three specialists on the same brief and you are not tripling the effort. You are combining three different networks that barely overlap, because each was built in a different part of the same industry.
The practical effect shows up in the first fortnight. Instead of one person working outward from one starting point, you get several starting points at once, and the candidates who surface early are the ones who would otherwise have taken a month to reach.
It also removes a failure mode nobody talks about. When one recruiter has a bad month, is ill, or gets pulled onto something urgent, your search stops. When several people are on it, the search does not depend on any one of their weeks going well.
The objection, which is fair
Several recruiters usually means several agreements, several sets of terms, several people calling you, and the same candidate submitted twice by two firms who then argue about who found them. That is a genuinely worse experience than one competent recruiter, and it is why most employers stopped doing it.
The fix is not fewer recruiters. It is one agreement, one account manager, and one person deciding who works the role and reading everything before it reaches you. You get the reach of several networks and the experience of dealing with one firm.