Although I'm a major Dylan fan, I'd say that John proved with "I am the Walrus" and "Across the Universe" he could write as profoundly as Bob's most psychedelic/beat-inspired stuff. I'm not sure Bob could ever write anything as simple and direct as Plastic Ono Band.
Melody-wise, Bob ain't even close. He filched alot from trad tunes and even the Beatles (Fourth Time Around). He's more of a blues guy. I don't think Bob could ever come up with melodies as compelling as Yesterday, In My Life, Hey Jude, Something, etc., etc.