Okay, I see what you are doing, but need to clarify something.
First, when you uncheck "sync music" it will delete all music form the iPhone. I'm okay with that, in fact this is how I solved the problem many iOS's ago.
Second, please clarify whether in your fix you select sync "entire music library" or do you choose "selected albums/genres/playlists" which means you need to manually select everything from the list below that.
I've got lots and lots of music and would require a stiff espresso or two to manually select everything. If would also seem that if this method of selecting individually is the solution, one might need to make selections under each tab for album, artist genre etc as well for them to come over.
What has been your experience?