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.
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.
That is also true for the overly simple object model of Perl 5, it is more like an OOP construction kit, which enables things like Moose which has for almost 15 years provided Perl 5 with a very flexible object model.
It would be very interesting to know if anybody knows of similar systems for other languages?
Large OO codebases can be downright nasty to navigate and while I have never had the opportunity to use something like Moose for large scale projects I imagine that's where it would shine.
There's a kind of elegant flexibility to that, but it also makes it really hard to program reliably in the large, to build useful tooling, or even to glance at a function and know what you should pass it.
Beyond that, classic Perl was full of things that make it quick to write small programs (as CGI scripts were at the time) without a lot of boilerplate, but which don't scale up.
(Perl 6 is very different, and has an almost comically flexible/powerful function signature system (https://docs.perl6.org/type/Signature). Whether or not you like Perl 6's stuff, it's nothing at all like Perl 5's.)