Paradosis: Too easily disprovable? I don't know how in the world you could believe that the gospel of John today is a coherent single work! Aside from geographic schizophrenia, there is idealogical disparities, linguistic differences, and stylistic shifts throughout.
Ever read Fortna's The Fourth Gospel and its Predecessor? Even without it, it's still possible to discern at least three different authors writing at three different times within the Gospel of John.
1)The Signs Gospel
2)The Jewish Christian Editor
3)The Fourth Evangelist (often called the Ecclesiastical Redactor)
Within the first chapter, there is enough evidence to say that there is more than one mind at work, or at least to suggest that, if there is only one author to the entire text, he's a terrible writer.