> The idea that users can reliably supply their own vendor libs/execs for applications is a bit of a fantasy.

That's why package managers and OS repos exist. Users shouldn't have to even be aware of this sort of stuff. In this case, though, when the application starts trying to download and install its own dependencies at runtime, instead of everything already being sorted out at build time, the user is made aware of dependency resolution, and now has to deal with the issues involved.

> This is especially true when it comes to open source work. Dealing with weird edge cases because the user has a version of FFMPEG installed that, for whatever reason, is missing h264, is work that nobody asked for.

And that's what config tests at build time solve for, and have solved for decades.