I do like Two Against Nature and Everything Must Go. To me, they sound like classic Steely Dan; the gap between them and the original run isn't obvious at all. Maybe a little, but not a lot, not like some bands which reform after 20 years or whatever.
Nope, Becker's solo albums don't thrill me, either. It takes the two of them to make it any good. Where do you get the figure "10%"? Even if Fagen does the writing and Becker mostly just shows up and plays guitar, the two of them have a chemistry together, and somehow that comes through in the final product.