To be pedantic it's guaranteed to be fully reality compliant in regard to how many EXTRA LINES of code are required (which was the context of the all caps assertion you've quoted). As Zoffix showed, it takes zero extra lines. Clearly, no language can do better than that.
But perhaps you're asking if any language can do better than the best that Perl 6 can do, assuming we're counting characters instead of lines.
Before trying to answer that, it's important to be clear on what is actually the best Perl 6 can do.
The two word solution Zoffix showed directly following the "THERE'S NO ..." slide is not the "best" Perl 6 can do.
Better is the single character operator » which Zoffix covers near the end of the talk.
That would be hard to beat but Perl 6 actually goes even further than that for what most Perl 6 folk call "auto threading", namely auto threading of junctions. This latter arguably requires zero extra characters. See https://docs.perl6.org/language/glossary#index-entry-Autothr... for more details.
In summary I'm pretty sure no language will ever do better, where better is about number of extra lines OR EVEN CHARACTERS, than zero. :)
I'm curious as to how reality-compliant this statement in regard to inline auto-threading support.