BTS

i dont think it exactly downgraded, it just changed. i think you just enjoy their older music more as a genre. music taste is subjective, just like how some may say it got worse, some may say it improved. it really depends on what you like and what you dont. of course, there are some objective aspects of music (such as pacing/flow, tune, all that and overall harmony), but when it comes to bts (i literally know every single song of theirs from debut to now, including unofficial ones and a lot of predebut ones), not much has changed. so i believe that mainly the issue in your head is due to your subjective view of certain music genres, not the overall objective quality of music.