"As individualistic Westerners we often operate under the presupposition that "Paul alone" is better than "Paul+others". It is assumed that ”pure Paul” was more inspired than anything written in collaboration, and certainly more than a passage written by another. The underlying presupposition is that anything not solely from Paul somehow dilutes Paul. It is assumed Paul was the "Inspired One" or the "More Inspired One," and therefore anything added to Paul detracts from this "pure Paul". However, we need to let 1 Corinthians remind us: the 1 Corinthians we consider inspired is not the 1 Corinthians written by Paul alone but Paul and Sosthenes (1:1) through a secretary (16:21)."
Richards, RE, (2004), Paul and First-Century letter writing, p.120.