It seems like you're trying to argue that Nujabes is more talented than DJ Premier, but I think you really just prefer Nujabes's style to DJ Premier's. Nujabes creates a more atmospheric mood, while DJ Premier creates a more rugged, street sound (which is why Nujabes wouldn't compliment Nas or Biggie. Guru could work). Neither style requires a higher level of talent to execute in general. Who you think is better really depends on a combination of who's actually more talented and which style you prefer. Personally I don't really prefer one style to the other, so I think DJ Premier is better because I think it takes more talent to execute his style the way he does. Comparing Mass Appeal to Feather is an excellent way to show why I think DJ Premier is better. They were both constructed in a similar way. They both used an inconspicuous sample that wasn't part of the main melody of the original song (Mass Appeal from Horizon Drive by Vic Juris, Feather from Love Theme from The Robe by Yusef Lateef). Neither sample would be an easy catch for any producer, and they're both brilliant sample selections. The difference is in the way they used those samples. If you listen to Love Theme from The Robe, there's a clear connection from the mood Yusef Lateef set to the mood Nujabes set on Feather. The same connection doesn't exist between Horizon Drive and Mass Appeal. DJ Premier took that sample and completely made it his own. Nujabes was great at hunting down samples that complimented his style of production. DJ Premier can pull a sample from any kind of track, and flip it into his own style. That's why DJ Premier is better.
Also, you're kind of displaying the typical inferiority complex that exists in most hip hop fans. By referring to Nujabes as "a modern Beethoven," you're implying that DJ Premier is a lesser artist than Beethoven. I think it would be better for Nujabes to be a modern DJ Premier. What makes Beethoven a better example of musicianship than DJ Premier? I assume you're more a fan of hip hop than classical music, so shouldn't you consider an elite hip hop producer to be better than an elite classical composer? A while back, a question was posted here in the RHH section asking what the greatest album of all-time is, regardless of genre, and almost everyone named an album that isn't hip hop. Coming from hip hop fans, that's sad that we can't accept our own genre as at least an equal form of art to other genres.
Sidenote: You completely butchered Nujabes's birth name. It's Jun Seba.