Since DK does let you do 2 people, technically Mario can be said 'does it better.' Even NSMBU has a few levels that were specially designed for only 1 person and don't work with multiplayer. I played DK only in multiplayer and I'd say its perfect the way it is, your friend won't be able to do some sections, but thats fine. I wouldn't change it to be more multiplayer friendly.
My point was more that it was a questionable merit to have. The multiplayer is what holds NSMB back.