That was the point of the first few paragraphs at least, but unfortunately the actual review is much longer. The point doesn't seem to be especially fair to me for two reasons:

First, what one is aware of is not necessarily what one regards as relevant to the topic at hand, and the statement was only that Dennett did not think anything before Descartes was especially relevant to his own view of the matter. In an earlier work, Consciousness Explained, Dennett discusses at numerous points some of the models of the mind entertained in the platonic dialogue Theaetetus for inspiration and comparison, so he's clearly not completely unaware of all philosophy before the 17th century. From reading several of his papers and books, there are other examples to this effect, but I don't want to belabor the point. It does not seem at all unreasonable for someone to judge a number of approaches or prior developments irrelevant to present concerns.

Second, this sort of accusation is fundamentally unfalsifiable, and can be made about any field. From the current front page, you might perhaps run across someone who claims "Anyone trying to study compilers without having studied the history of the Oberon Compiler will be running in endless circles". I would not be unsympathetic to such a person. The Oberon Compiler seems to have embodied quite a few really interesting and innovative new ideas, even ones that haven't been followed up on since. However, such a person would still be being fairly silly. It is a generally tolerated delusion for one to assume that one's own field of knowledge, domain, and preferred schools of thought are absolutely crucial to correct thinking on some matter. Nonetheless, the history of the human intellectual edifice is one of continual reinvention and independent development of numerous important innovations. There comes a point when any professional, must start developing their own arguments and responses rather than just playing field historian.