There are many ways of categorizing a song, most of them subjective.
It would seem that putting labels on them and assigning them to various boxes is merely a convenience that allows a vast overlap.
Putting rigid definitions to somewhat arbitrary divisions results in an argument just waiting to happen. Better to just accept that different opinions exist and not get het up over it.
While academics may wish to discourse the bulk of humanity merely wishes to listen, or a small minority perform. If the song is not popular it dies. In the corpus of pop how many pass the old grey whistle test?
"yesterday" is over 50 years old. Do we regard it as pop or folk.
"Dancing queen" is equally as popular but I would argue it's impact is ephemeral whereas Yesterday plays on deeper emotions and to my mind give it greater longevity. My thoughts-others may have other conclusions.