There are two meanings of "producer" at play here: a) he who cuts a beat, b) he who produces an album. Kanye was limited yet very successful at A, and he may be the best in his field at B.

Kanye may not be the world's best rapper, but he is no slouch, and to be producing (both meanings) in the capacity he does at the same time is staggering. I like to tell people it's as if Martin Scorsese played the lead role in all of his own movies.

From everything I've read, Rick Rubin arrived late to the project and edited a mountain of work down into a short album.