"few applicants, most pretty good" was true for us as well when hiring Haskell developers at Freckle (https://tech.freckle.com/) - in some ways it was scary: we're away from the herd, the numbers aren't on our side, what if we ever need to hire large volumes of people?
Instead of getting 200 JavaScript devs in the pipeline, you would get maybe 10-20 Haskellers. What if the person you're looking for is not in that pool? Intuitively, you assume that more is always better.
In other ways it made filtering through candidates quite simple: half of the people who applied were really good, the other either language astronauts or folks fascinated with the tooling who didn't genuinely want to move fast to produce commercially-viable software, they wanted to tinker. You just needed to figure out which bucket the person was in.
Most systems are not large enough to need 200 developers. Even when they are, you hire those 200 over time. If you have 200 developers (or 200 anything) you need to have a good training and mentoring program.
Language is not the problem. If someone is a senior developer (not just has the title because of years of service), you can teach them Haskell on the job for little cost. Sure it will take them a few years to be an expert in the language, but most problems they need to solve don't need language experts, just someone good enough. And Haskell is a different language, most often you are hiring for a language that is only slightly different from ones they already know.
In other ways it made filtering through candidates quite simple: half of the people who applied were really good, the other either language astronauts or folks fascinated with the tooling who didn't genuinely want to move fast to produce commercially-viable software, they wanted to tinker. You just needed to figure out which bucket the person was in.