Sorry, but that is so UNTRUE!! MOTOWN...almost ALL OF IT was FABULOUS!! EVEN disco was pretty good....and the 50’s were FAB!!
Sorry but it is true. You’re picking genres and ignoring that there was other stuff (and frankly most of Motown was the same old indistinguishable girl band crap over and over).
Here’s the top 100 for 1967 http://www.musicoutfitters.com/topsongs/1967.htm generally considered a very good year in rock and a big Motown year, and the number 1 song of the year is Lulu with To Sir With Love... pap.
You call out disco, here’s 1979 http://www.musicoutfitters.com/topsongs/1979.htm big winners are My Sharona (OK not horrible, not great either), Bad Girls, Le Freak, do You Think I’m Sexy, and Reunited... crap.
1950s, http://www.bobborst.com/popculture/top-100-songs-of-the-year/?year=1957 well #1 in 1957 was a half way decent Elvis song, then Pat Boone gets his highly synthetic fingers on #2 AND #6, good year for Pat, bad year for music.
Sorry reality is reality. You REMEMBER the great stuff from that era (or it’s been remembered by enough people for you to find it if you’re not old enough to have actually been there), but there was plenty of not great you (and/ or others) have conveniently forgotten.