I'm not familiar with recent versions of Rails or its authentication situation, but whenever I hear this said about some mandatory functionality of a system, it

I'm not familiar with recent versions of Rails or its authentication situation, but whenever I hear this said about some mandatory functionality of a system, it sounds to me exactly like "We haven't yet figured out how to do ___ well". It reminds me of the old days when I'd get a library which would say "We want to be flexible, so just pass in any memory allocation function here!", or Linux distros that said "We want to be flexible, so just write any boot script here!" Then a year later, some competitor ships with a default, and everybody switches over to that because it's obviously better (and you can always customize it if you need to). Especially so with Rails, whose entire existence seems to be picking good-enough defaults.