Martin's criticism of Lost's ending has nothing to do with the rigors of producing a television series. His criticism was regarding the finale's narrative flaws, and seeing as he's been working professionally as a writer in both the literary and television circles for almost forty years, I'd say he's more than qualified to comment.
Uh... Nobody needs to be working professionally as a writer in either literary or television circles to criticize a show - all they need to do is *WATCH THE SHOW*... While Lost's ending worked for some people, it's also true that it did NOT work for several other viewers.
However, I can't see in the Original Poster's post what exactly Lindelof said back. Anybody care to give a link?