You're somehow still missing the point. Lyricist is not used as a synonym for song writer in hip hop.
Song writing ability - is one of those terms that doesn't really mean anything to me. What does it mean to you? Like the ability to do something off the beaten path? I Gave You Power? One Mic? Rewind?
Or does it mean the ability to craft a catchy song that will get radio play?
IF you're analyzing Rappers and talking about skill, song writing is an essential ability.
It's the reason why so many "Avante-garde" underground cats wind up spinning their wheels releasing mediocre SONGS with good/great lyrics.
Pac wasn't just good at writing his lyrics, he was able
to create SONGS.
Nas, Jay-Z, Mos Def and many other greats in this genre and others, understand this.
They aren't just supreme lyricists who have sixteens that are
little islands, they understand setting mood, the power of the hook,
good beats and combine that with telling stories, bragging, exploring themes/concepts.
Song writing is already difficult as it is,extend that to a full project
with an overall theme and you see what separates Nas from all of these
cats who could probably rap circles around him but have mediocre discographies.
Canibus (one of my favorite rappers period) just lacks this ability.
I'm certain my dude in his prime could eat any rapper alive but ever since his debut he has consistently shown that he lacks critical skill in "Song writing".
With horrid hooks, inconsistent production and too much focus on dazzling with
metaphors, punch lines and word play.
For an example in understanding the power in knowing how to structure a song compare :
"Rip The Jacker" against other work in Canibus's discog !
Having a producer oversee the project who understands this allowed
him to not only breath as a rapper and showcase his skill in writing
but create an enjoyable listening experience.
I'm certain you wouldn't be a Nas fan if he still had the same skills
but couldn't write records like One Mic, I gave you power, 2nd Child hood and the like.
It's the same reason people love Pac, he was not only nice
but he could write songs with a lot of different concepts and overall
feel while still making them enjoyable.
I believe that song writing matters a great deal, I'd wager Nas wouldn't
be relevant right now if he wasn't as skillful as he is at writing songs.
He'd be like many other lyricists lauded for their use of literary devices but
largely ignored when the conversation shifts to MUSIC.