Well, that's one way of looking at it, the one I've been thinking of is that the distribution of competence is similar in all languages, but with niche ones it becomes easier to filter because good applicants do not disappear under deluge of bad ones.

There's also survivorship bias in sticking long enough with programming to actually look for jobs in niche languages or accept that you will be taught on the job, something that I've seen only with either experienced or more open-minded/educated people