They are different. Namespaces are syntactically enforced and you can opt-in or out to names. To have syntactically validated qualified access.

Naming might go well and have the same utility, but you never know what evil things are going on in all those headers, redefining each other's symbols and yours.

You seem to be focusing on specific problems with C/C++. I don't really care about that, all I'm saying is that prefixing names are equivalent to placing them within a namespace, in practice, and theoretically come to think of it. You can easily define a bijection between namespaced symbols and prefixed symbols. Requiring the full prefixes are simply a tad more verbose, essentially equivalent to using a fully qualified name for symbol.