Actually, Mr. Kay wrote an essay post of far more eloquence than I could manage in response to Dave on his forum. I don't think we can reprint it here, but IM Erfael if you're interested.
"Dave" is what I've come to call a traditionalist, a rather rigid group which thankfully is not too large. Of bigger size and louder vocals are the reformers, who shoe-box from the opposite direction -- there's a box labelled trash and they put you in it, while putting authors they like in the artist box.
The authors in the deep genre discussion -- and there are some heavy hitters there, plus editors -- are not really proposing traditionalist or reformer thinking. They seem instead to be responding to those groups, and with a fair amount of frustration. I sympathize, because this is a very old argument. Dawnstorm put up a link in the Scott Lynch thread in the Fantasy forum to Lynch's blog, and the most recent item there has him telling about how Ursula LeGuin had to deal with reformers over Earthsea long ago. In the 1980's, cyberpunk sf was the hot trend and this spilled over into claims that only contemporary fantasy -- elves with computers -- was worth anything from groups of fans. Periodically in sf, there's much debate over what should be allowed to be called sf and what is otherwise masquerading junk.
If it's just a matter of authors talking about why they write fantasy, and the value of various mythological elements and themes, then it might be helpful. But the presentation of the "deep" concept is that some authors are deep and some are not, and that deep is better -- a standard of quality, creating a caste system. If you are trying to get everybody into the pool, telling them that part of the pool is a swamp is not condusive. It's not that I think these authors shouldn't talk about these issues, but I think the discussion will get lost under the idea of who can get the gold star of "deep" and avoid the deadly badge of "comfort."
Fiction's "marketing paradigm" is symbiotic, not competitive. That is essentially what a category market is -- a large, symbiotic block allowing 20 authors to be presented instead of 2 to an audience that will buy many such authors, rather than just 1, the most visual symbol of this partnership being the sff sections in bookstores. Publishers also package groups of mid-list authors together to promote and sell them to booksellers. Authors can team up to support and promote each other more effectively than they can alone.
Authors do get this, which is why they get worried when authors or groups of authors get trashed. Take that Venom spat at a convention a year ago or so. This poor author reads an excerpt of another author's work that he finds strange and kind of funny, has a private conversation with pals about it, and gets jumped on visciously from all sides on the Web. Why? Because of fears that he hurt the Venom author's livelihood, where upon he was threatened with damage to his own livelihood. This kind of thing doesn't help anybody, but it does show the sort of fear that's going around.
So what then can be done to help authors when fans argue that they should be shoe-boxed and that they belong in the inferior shoe-box? I don't think there's an easy answer for that, or we would have found it already. But I can tell you that social caste hierarchies just reinforce shoe-boxing and don't help anybody much, in my experience.