I can only imagine working with generated parsers to become more difficult, if the syntax of a language is highly ad-hoc or irregular, not elegant like concattenative, or lispy languages, or Smalltalk style, which is ironic, given Ruby's history. Maybe they added too many bells and whistles.

In every other case having a grammar in form of parser generator macros should be better and preferrred, since it is well portable to other languages and tools and lends itself to be more readable (with good naming).