Here's the thing, at least with respect to pop/rock music. Music school can teach you certain stuff, like about playing your instrument and arranging. But it can't teach creativity and inspiration. The ones that have that, don't need music school (or leave it early), and the ones that don't, won't gain it, in a meaningful way, from music school. The weakest part of music school is songwriting, always.
There are plenty of songwriters who incorporate "sophisticated" musical elements into their compositions (e.g.,Paul Simon, Brian Wilson, Lennon/McCarthy, the Steely Dan guys) and plenty who use simpler elements to make music of the highest caliber (e.g., Dylan, Springsteen, Taylor Swift). None of them had anything to do with music school.