Production Values

This article from the Canadian Broadcasting Company discusses the problem of prolificness: do otherwise good writers get down-graded in the literary pantheon because they're perceived as overproducing?

Prolific authors mentioned: Alexander McCall Smith, Ian Rankin, Agatha Christie, Peter Robinson, Stephen King, Elmore Leonard, John Grisham, Maeve Binchy, Anne Perry, John Updike (about whom David Foster Wallace is quoted as having said: “Has the son-of-a-bitch ever had one unpublished thought?”), P.G. Wodehouse, Joyce Carol Oates, Neal Stephenson, William T. Vollmann.

The journalist should probably have mentioned romance authors Jayne Ann Krentz (a.k.a. Amanda Quick, a.k.a. Jayne Castle) and Nora Roberts (a.k.a. J.D. Robb), whose output is so high and whose names are so branded that they've taken to multiple noms de plume.

The article goes back to Wodehouse, but I would be interested to see someone look at how the prolific author was considered earlier. Anthony Trollope's admission that he worked by the clock damaged his reputation, but Scott and Balzac's writing their ways out of debt was figured as almost heroic. What book/year ratio was considered "normal" when?