The term "songwriter" is kinda hard to define.
Is a songwriter a "composer'?
Is a songwriter a "musician" ?
Can a drummer who doesn't write lyrics be a songwriter?
But, anyhow, I do call myself a "songwriter" from time to time and over the years I have "composed" close to 60 "songs". Some are instrumentals. On top of that I wrote radio Jingles for a few years. ( are those songs?? no they are Jingles)
Back when, all you needed was a guitar or piano and a tape recorder. That was all it took to make a "Song Demo" to submit to a record label or to your band mates.
Things have changed and music has changed. Thanks to software we now have music ( songs) that can be made by non-musicians.
Most of this software has evolved along those lines. Sonar is used by a lot of old school musician/songwriters/performers like me but I would hazard a guess that the majority of users are more the producer types and people with very limited musicianship. This is fine.
The only difference is that I could record a whole album or movie score without software, the others cannot. But software has made my life easier too ( I think?)
So to me the real question would be:
What tools does Sonar offer the Traditional Composer musician.
What tools does Sonar offer the Modern Producer non musician.