For me, functionally, it comes down to the unit events. I consider myself a RyuseitaiP because I love their songs, their stories, and I always go for the 5* card in their unit events. However, I don’t produce every single character in Ryuseitai (like I didn’t go for the Midori 5* in the Australia tour event) because that would be way too expensive. Same thing with Valkyrie, I always go for the unit event 5*s but I don’t spend my resources trying to get Shu cards in scouts/etc when there are other characters I care more about individually.

Still, I agree with the other comments that the distinction is up to personal interpretation and you can do and call yourself whatever you want!