OK... I see the point of the OP and I agree. But I also see and understand the dissenting POV that composing and writing are essentially the same.

I personally tend to divide composing and songwriting along the lines of the OP.

To me songwriting is a simpler, more basic form of composing, while composing in it's own right is a bit more detailed and intensive form of songwriting. I place compositions by writers such as Bach, Mozart, Handel, firmly into the composer class while placing writers such as Lennon/McCartney, Guthrie, McDill, into the songwriter classification.

There is a huge difference between a song and one of the compositions of the masters. Structure, use of chords and extensions, and length to mention just a few things. They are different disciplines of writing and require certain skill sets to do effectively. The common thread is that they both involve music and the thought process to create something beautiful with a limited number of notes.

I think perhaps there are a few writers who can successfully cross that line. Jeff Lynn (ELO: Out Of The Blue) and Ian Anderson (JT: Thick as a Brick) are two I can think of that can get close.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.