I don't understand, musical notation is text though so how can it be superior to itself?

For complex music, sure, but if I'm looking up a folk tune on, say, thesession.org, I personally think a plain-text format like ABC notation is easier to sight-read (since for some instruments, namely the fiddle and mandolin, I mainly learn songs by ear and am rather slow and unpracticed at reading standard notation).

Yes. And I create and manage the musical notation for over 100 songs in text, specifically Lilypond.