But they can be still be judged as composition. It doesn't matter whether music is produced by a person writing out a score or is spontaneously improvise or is written as chord over a lyric sheet. Ultimately every piece of music can be reduced down to notes on the page after the fact. irrespective of how it was produced even if the songwriter doesn't know how to read and write notation, the end result is music that can be notated
If rock music is inferior to classical music (which you have argued) due to lack of substance from a notes on a page point of view
Then surely one pop song can be inferior to another pop song due to the same rationale that you used to rate rock music to be inferior to classical music.
There's no reason to create a different standard for different genres of music