Let me put it this way, in the 70's/80's, unless you were a novelty act, you had to be able to sing, play an instrument or write a hook. I know there was a lot of crap in those eras, but take a look at Oo Nana Haya or Chirpy Chirpy Cheep Cheep. Yes, they are crap, but at least you get the feeling they put some effort into the music. The 80's had a lot more style over substance (from what I can tell, I wasn't born in the 80's) than the 70's but it still took
some work to get to the position where you you could release garbage, and the "Music video" songs had good music videos unlike todays softcoe porm videos.
The reason so many people hate Justin Bieber (and pop musicians in general) is because, although he can strum away a few chords, he hasn't done anything to show he has anything to offer. He doesn't have revolutionary video concepts, he doesn't have complex instrumentation behind his work and he doesn't have message to bring to the table.
The music industry seems to have decided that instead of just waiting for the next Hendrix or Beatles to emerge they can just tell us that the current artists are the best thing music has to offer, so it isn't really a hatred of them as people, but of what they represent. Which is pre-produced "Musical Geniuses" or "Controversial and Cheeky artists" when everything they release or do seems like an advertisment for their image rather than an actual song.
It's the same as in the 50's when after Chuck Berry was in jail, Elvis was in the army and Little Richard was in the church artists like Ricky Nelson got promoted as Rock and Roll stars.
pink floyd (maybe, thats kind of stretching it. it would have to be a scetchy disco tech), E.L.O, Abba, rolling stones, etc.
I wouldn' t call Floyd and the Stones disco bands, they did have disco moments.