Defaults to. You can tell it to compile yourself, if that matters to you. I don’t see what the issue is here. Why is it a problem that it defaults to binary distribution?
> The biggest problem is that the defaulting to binary distribution also means that building from source is unsupported.
I don't think it means that at all. They're both clearly supported by homebrew — one just happens to be the default. You can always use -s or --build-from-source to build whatever package you are installing.