I agree with you ENTIRELY. I do wish she realized how in tune with melody she often is... I get the feeling that she chooses melodies and THEN determines what feeling to express in her lyrics, rather than starting with a feeling and some rough lyrics & then working her way out from that. She's picking melodies lately based more on their appeal, when she's SO SO SO very good at writing or choosing melodies based on how they FEEL.
Letter is one of my favorite tracks on PQ, that was one of the reasons I chose it for the album's release day rather than the title track (especially since PQ had other days that applied, like when the Peach John CM debuted and when the tour started, you know?). All the songs' dates have meaning (well, not all, but MANY) either to ayu personally or based on a release or CM or tie-in.
