YOU are the one misinforming, it would seem. Granted, I don't work with perl (5, never tried 6) for about 15 years, but most criticism of it seems to align with my experiences back then.
[0] http://mvp.kablamo.org/basics/functions/
Edit: The second [1] also recomends the @_ method, and the third [2] the shift method. Did you even read your own links?
[1] https://perlmaven.com/subroutines-and-functions-in-perl [2] https://learnxinyminutes.com/docs/perl/ (search for subroutines)
> WARNING: Subroutine signatures are experimental. The feature may be modified or removed in future versions of Perl.
Which is to say: a lot of the reason they're still experimental is because Perl's commitment to backward compatibility. Other languages might have said "oh well," but Perl 5 said "oh, an unintended consequence that might break real uses in the wild; we should wait another year."
On Perl6 those are officially supported, so I imagine they work.
Sorry, you are misinformed. That hasn't been true for a long time, see http://p3rl.org/Kavorka::Manual::Signatures
Other languages would kill for this kind of beyond-complete maximum overkill feature set.
> This page gives a good overview of the situation: https://perl101.org/subroutines.html
No, it doesn't. That page is not wrong, but incomplete and teaches the wrong stuff, wouldn't recommend. Instead see http://perl-tutorial.org/ for recommended tutorials.