They aren't saying developers are unproductive. They are saying teams of developers are unproductive. In the words of my great grandfather. "one boy is one boy, two boys is a half a boy, and 3 boys is no boy at all"
I don’t know. If someone told me “there is nothing less delicious in this world than your turkey casserole” and you came along and said “they aren’t saying your turkey casserole is undelicious,” I’d be inclined to believe you misheard something.
