Software licenses exist because copyright enables author to dictate terms. Without that, there are no software licenses. This is where the "without copyright, there is no OSS" comes from.

> Their weight is irrelevant.

I think we're having different conversations. The only thing I'm talking about is whether terms can be legally enforced without copyright.

I'm not sure what you're getting at, but it seems to be something like "Permissive licensing is basically like public domain." I don't agree with that line of thinking because of the attribution requirement in permissive licenses, but if that's what you're getting at, I get what you mean.