Magical Mystery Cure is the episode with more songs in the entire serie, if I’m not wrong. So, winning a music award for an episode that in in essence a musical is like winning the lottery with several numbers purchased ,that doesn’t mean they are bad, though. But I would prefer that other episodes songs which are better (This day aria, for instance) would get that recognition.
Also, the music wasn't why people were/are yelling "RUINED" and everyone knows it…

"The episode had (a) song(s) that won an award, therefor the episode was good"

I think that's bad logic. We can like the songs without liking the episode, even if most of the episode was songs. We can also hate the songs without liking an episode as well, but that's each person's opinion as well. Critics' tastes also are generally different than a lot of peoples', so a lot of people don't give a damn if some dudes in another city have an opinion, whether or not people pay them to give it.