I think it would be closer to say "Perl 6 and Perl 5 are two completely different languages, and have about as much in common as Ruby and Perl 5". All the languages in that sentence are Perlish languages, so to me it conveys the relationships better. Perl 6 definitely has a lot to do with Perl 5, especially the mistakes therein. If anything, it's the most Perlish of them all.