Some more I have, these are mostly about my country's music:
Rata Blanca, Hermética and the rest of early Argentine metal exponents are trash and bland, and only die-hard nationalists (in the music sense) listen to them despite there being thrice as awesome bands in every other place. Same can be said for most national rock bands like Soda Stereo and Los Piojos.
Charly García is the most overrated musician in the country (not counting folklorians), mostly by old tards that keep sucking his dick for having written some lame political songs. He isn't even half of the musician people think he is, and he's being milked to death by the industry even today: his new album is absolute garbage.
Trap is the worst trend to ever exist here, probably the worst slop in music that's even being used by political candidates to appeal to youngsters.
To metalheads: buying 400$ worth of bands' merch every month doesn't make you better than anyone, and certainly doesn't mean that people who just like to sit in his house and listen to music digitally is worse.