I never considered KRS One a super lyricist, he's a good solid lyricist, same ranking I put LL in. Difference is, KRS has really high peaks of lyricism that LL doesn't have (CIA verse, Brainstorm, Stop the Breaks, etc). I think he was actually way better lyrically later in his career, but he did have some real stand out verses in his prime as well. LL was a good standard lyricist. He never Wowed ever. KRS has at times. But I agree, compared to the Rakims, Kanes, G Raps neither are elite lyricist.
I love KRS flow and delivery because they're so versatile. Pretty much LL rapped the same style every song and every verse. I get it, if it ain't broke...but still.