The main reason to learn Raku at present is simply that it's profoundly different from most other things out there-- there's no particular "killer app" that's emerged for it, but it's unusual enough that this might happen yet (no one expected Perl would be critical for "Web 1.0" and the Human Genome Project...).
Some Raku features:
(1) it's numeric types include true rational numbers, so there's less chance of being tripped up by floating point approximations (e.g. 2/3 is really 2/3, and if you multiply by 3 later you get precisely 2). It also does big integers by default: you're less likely to have overflow problems.
(2) Raku's regular expressions have been redesigned from scratch, and it ships with expanded capabilities to compose them into larger structures called "grammars": Raku is a uniquely powerful tool for writing special-purpose parsers, ala domain-specific languages. (Note: this is how Raku parses itself-- it's not implemented in the usual lex and yacc style.)
(3) Extremly convenient features for handling CAP (concurrency, asynchrony, parallelism), possibly the easiest to use of any language.
As for Perl (meaning the original, Perl 5), it's vastly superior to traditional bash scripting because all the components were brought into one process where they could be made more consistent and talk to each other easily.
How Perl compares to Python is a little difficult for me to answer: I prefer Perl, but I could be biased on this one, and there's no question Python has quite a bit of momentum at present in a number of areas.
