I’m not sure what “more” productive means in that context, in any case. I suppose that if you’re writing things with other people, and you therefore write a smaller percentage of the words of each of the things, you can write/publish more things — but I’m enough of a humanist to be intensely skeptical of that way of assessing productivity. (Although I did heave a big sigh of jealousy when a major scholar in my field, on the verge of retirement, was introduced as having written “106 articles and many books.” But then, she’s co-authored most of her work, including a book on collaborative authorship.)

And, do you already know Lisa Ede and Andrea Lunsford’s Single Text/Plural Authors (SIU Press, 1990)?