De-facto standard extensions for recursion and variable-length look-arounds have existed for ages; the word “regular” in most regular-expression engines is there for historical reasons. I first read about this in Apocalypse 5: Pattern Matching by (he loves his biblical terminology).
I would like to just use Raku rules for a concise way to describe more advanced grammars; I’d then just keep my regexes to the PCRE subset that’s common between Google’s RE2 and the Rust regex crate. I doubt they’re both “regular” but both guarantee linear time matching. Part of the reason I don’t do this is portability. Not everything runs Raku, but almost every platform has a regex engine with the features I need.