"Big clue: You don't need a book to listen to music."

True, but you can say the same thing about stories poems and news.

On the other hand, a proficient reader can "hear the page" when they read a musical score.

These days most people get their stories off youtube and the TV and they get their music from mp3s and the radio.

You and I can, if we want, convey concepts to each other in words.

Musical notation, theory, literacy etc allow musicians to do the same thing wityh music without having to write reams and reams of cumbersome descriptive words like the ones you and I are using now.

If you want to learn to speak chinese, it makes sense to learn some characters at the same time so you can write to your chinese friends etc.

I think the problems you describe are due to a non creative education not down to whether kids are able to read.

When kids experience of music is to only play (say) exactly what they are told, it means they get no practise being creative or developing their ear.

Sad indeed, but not the fault of theory or notation.