To quote Apocalyse 6

Please note that the Apocalypses are mostly historical documents. S06 is what you should consider.

but isn't the Perl 6 solution using references as well?

Yes. Under the hood, every argument passing uses references, unless the parameter is decorated with the is copy trait. Unlike in Perl 5, these references are write protected by default.

So Perl 6 still passes references, its just that the syntax no longer requires the \.

Not only the backslash, but also the dereferencing inside the subroutine. Since (nearly) everything in Perl 6 is a reference, references are transparent, and don't require special syntax on either side.