I never understood the appeal of this talking point. It’s just an accounting trick that moves the complexity to the standard library.

For example, SmallTalk is a class based OO system, yet this postcard doesn’t slow you how to create a class.

Yes, Smalltalk's syntax fits on a postcard - and it's possible to go even more minimal than that, e.g. Lisp or Forth.

OTOH Ruby doesn't need a postcard, it needs a full poster.