You ain’t wrong. The level of arrogance stinks. Especially when the author put effort into documenting the sources etc.
There do appear to be a lot of these know-it-all-but-contribute-little types around.
Maybe a few are missing, but simply asking, and I’m sure they’ll provide. If someone wants a better build system, they could volunteer to do it themselves.
Maybe edit and request a DM. Don’t put your email in a public location.