Man, way too many great points made here. I don't think anyone can say there is a right or wrong point of view. There's an old country song that says, "Do what you do do well boy, do what you do do well". Rather obnoxious hook, but the point is there.
I've been playing guitar since I was 8, self taught. I got some formal training in HS band. Raised on Hank Williams, diggin Pink Floyd, I was a mess. But all those influences show up in my writing. But, remove any of those components, and maybe I can't write melodies, maybe not lyrics. We write what we know, whether it's music or lyrics. But, I do feel strongly that if you can only do one or the other, you limit your resources to just collaborators. Nothing wrong with that, but you're just a little handicapped at that point. Personally, I'm blessed with the ability to do both, whether good or not. I have only recently discovered the pleasure of working with collaborators, and that's really the best of both worlds. Music, is just that, with or without lyrics. But lyrics without melody and musical structure, isn't music, YET. Not to say that it can't/won't be. I have yet to be able to look at a set of lyrics that someone wrote, and come up with a melody, or chord structure for it. I work at it, but it's not there yet. Now, give me a simple melody, and the universe explodes in my head. That's the way my brain works. Others are more blessed, and with different abilities.
I believe there's a place for all these people, as long as they are grounded in reality. I may never write a hit song, but I've got tomorrows Top 40 running through my brain as I type.
Swing hard, in case you hit the ball.

Peace,
Steve

What's another word for Thesaurus?
--- Steven Wright ---