It may well be that some relatively-little-used tool nontheless has a very significant use. Popularity is one factor within the mix, but only one.
We generally only refer to popularity after a formula comes up on our radar due to failing other sniff tests. To give you an idea for some of them:
1. Multiple subsequent releases without anybody bothering to update the formula
2. Historical problems with the package (flaky builds, complex build systems)
3. Historical problems with the upstream (patches ignored, unwillingness to cooperate with packagers, unreliable download servers)
Since homebrew is aimed mostly at technical types and devs, build tools themselves are probably fairly highly featured, but those are easy things to lose in large general-public releases. (Android's abysmally poor shell tools come to mind.)
Sounds like a pretty good basic set. The flaky builds criterion in particular seems like a strong signal of a low-quality upstream.