Isn't that something by design? Luckily, Raku does not use the hierarchical CPAN module flow and allows differentiation by author name and version. It is a major selling point.

Warning for a core feature will be read as a discouragement and cause more confusion. Could adding the author repo handle (e.g. from github) to the importable name space be a solution?

Well, the core feature is that you can add auth as metadata. Warnings will be issued if you don't, because, as far as I understand it, the one with the newer version will be used. The way I understand it, if two distributions provide Foo::Bar, you have to explicitly declare Foo::Bar:auth in the module if you want it to be used that way.