To me, it's mostly the presence of all new CS inventions in core. Like you don't need any damn libraries to paralellize stuff, just use `start` block or a `supply`. If you write accounting software, you'll appreciate built-in rationals so that 0.1 + 0.2 == 0.3, unlike so many other languages. Laziness is present in many things like lazy exceptions, string generation, and sequences: say (3, 9 … ∞)[^20] does not hang and produces (3 9 15 21 27 33 39 45 51 57 63 69 75 81 87 93 99 105 111 117), despite being an infinite sequence.
You also have grammars, more readable regex language, and superb object model. On a more advanced spectrum, with grammars and slangs, you can craft your own mini-languages for a specific domain where they would fit better; there's a nice little presentation by Damian Conway where he crafts an operator for quantum mechanical math that looks and functions just like the proper mathematical symbol functions: https://www.youtube.com/watch?v=Nq2HkAYbG5o
As for the langs you mentioned: I find a lot of similarities between Rust and Perl 6, although in some areas it seems Perl 6 folks did more thinking (like the .match stuff). They are however in different domains, Rust being a systems language; but you can use Rust libraries in Perl 6 via NativeCall if you compile them for C calling convention.
Perl 6 smokes Ruby and Python with its asynch/parallel/conc. support and more advanced object model.
As far as Unicode support goes, only Swift comes close to Perl 6; try to uppercase "ß" in Ruby, for example. Even if you to claim you only write software for English-speaking customers, you still have to deal with weird customer names for example.
For parameters you mention, many people notice they have to write fewer code in Perl 6. Personally, I found when writing equivalent code as Perl 5, my Perl 6 versions were TWICE as short. And I don't mean you golf your program to anything unreadable, but rather the provided primitives are... well, modern... so I don't have to reinvent them with more basic primitives provided by older langs.
What you'll find is performance is a bit crappy right now. Perl 6's stable got released less than a year ago so there's still a ton of work left to do in bugfixing and optimizations. I think that's what a lot of folks fail to realize that Perl 6 is a brand new baby language so trying to compare its performance to Python (25 years of work) or Ruby (21 years of work) or ES6 (tons of corporate interest) is a bit unrealistic at this moment in time.
In conclusion, one can list dozens of benefits, but I think at the end of the day, it'll all come down to which language better fits your brain and if you participate in a community, which community feels more like the folks of your kind. So far, anyone who I saw try the language say they loved it. The performance can use an improvement and that's what the core devs are working on. So, I think the steam is being gathered.