Let me ask you a question:
If you knew someone who only wrote 100 words a day -- and perhaps didn't work every day -- and who took five years to write a novel, would you automatically assume the person wrote a good book?
Then why would you assume that someone who writes 1000 words a day, and who writes more than one book a year, automatically writes badly?
Doesn't it actually depend on a number of things which has nothing to do with how fast the person can type or how much time he might have to devote to the work? I think the quality of the work has nothing at all to do with how quickly someone can get words down on a screen or paper. There are some very good slow writers, but there are a lot of really bad slow ones as well. There are some horrendous fast writers, and there are some very fast good writers -- Rex Stout is one of my favorites, and he was incredibly fast and prolific. So was Isaac Asimov.
There are good and bad writers in both camps. Ability to write well is not based on speed. There are a number of factors, including ability to edit, ability to imagine a coherent story, and the ability to write good prose.I think judging people's writing without ever seeing it, and based only on how fast they write, is a really egotistical prejudice.
I'm a fast writer, but I'm not a particularly good one. I'm working on my abilities, though. And I have learned that the more I write, the more I learn about the craft. Others learn in different ways.
I might never make it past the small press publications I already have. Or I may have a breakthrough and step up to the big leagues. I can guarantee, if that happens, it will be based on ability, and not how long it took me to write the book.
(This brought to you, of course, based on a post in Miss Snark's blog, where I have also posted this response.)