I agree with your post to a degree, in that his lack of producing a complete classic album from start to finish counts against him if your comparing him to say Pete Rock, Rza, Primo and Dre. However, while Kanye West is a good producer he doesn't do all he's beats by himself so I wouldn't say he's body of work is better than Just Blaze's at this point if anything I would say they are about equal.
You mentioned Marley Marl who hasn't been relevant for about 25 years, however, he had huge influence on both Pete Rock and Primo who always site him as a massive influence whenever they are asked state who they look up to. Nevertheless, Marley was surpassed by them and others in the early nineties, would have been intreating to see how It Was Written would have turned out had he produced that Nas album as was originally planned.
Dre hasn't done all his beats by himself now for 20+ years, I guess that just reflects how hip-hop has changed to degree, Timbo don't seem to do it all by himself now as well. It's just rare for one producer to handle complete projects these days particularly on big budget projects. Producers like Alchmeist and Madlib still do handle complete projects but that's mainly for underground rappers.