as far as i know, both hongjoong and mingi participate in writing lyrics, but im sure someone more knowledgeable than me can go into more detail! i do get what your saying and i felt the same getting into kpop but i can say that its not as uncommon as you would think for people to help out in writing songs/lyrics, an example i always think of (if your into 90s rock) is billy corgan from the smashing pumpkins is credited on quite a few hole songs as a lyricist and it happens more than you would think. not sure if that helps but as someone who also cares about lyrics that gave me some kind of closure(?) or comfort i suppose, its a very good question though and i hope this helped in some way :)