I can co-sign on this part of his premise. I worked for a music producer who has a number of #1 hits (Beyonce, Fergie, John Legend etc). He wrote >1 songs per day almost every day for over a decade.
His success ratio (hit vs placement vs nothing) was much lower than any mediocre software engineer trying to make working software over the same period of time.
It feels safe to say that in a 365 day period, a software developer can reasonably expect significantly more than one of those days to be used in 'working software' right?