Ah, but there are manuscript books by the millions available to us here and now; how many session musicians would actually be able to read the dots?

I know many who are considered perfectly able and competant musicians, some even considered brilliant, who are quite unable to follow even the simplest melody when it's written down.

Conversely, I also know many trained musicians who cannot extemporize or introduce new harmonies if they don't have a score in front of them.

LTS