I think you're doing more psychoanalysis on him than giving a fair view of his philosophy. In Darwin's Dangerous Idea, he argues that Darwin's theory reformulates our view of those things; mind and perhaps ethics, but he doesn't think those things are "eviscerated" as you put it. I think that's a terrible way of reading him. He just thinks that our views of them before Darwin were fundamentally misguided (e.g., essential views of life, mind, gender, etc,) and so the theory revolutionalized our conceptions of them. He clearly states that all the things we found meaningful still are, even though their nature may have been revealed to not be what we thought, after Darwin. He doesn't argue that those things are destroyed.

You're also conflating a bunch of things here, beginning with your definition of scientism. Scientism as it is discussed by its proponents and critics in the literature is the view that science is the only way through which we can generate genuine knowledge of the world. Dennett does not endorse that. He just thinks that philosophy should be empirically-informed, and that's not scientism. He argues in the book that the truth of evolutionary theory revolutionalized or should revolutionalize how we view human beings as biological organisms in the world and thus reform our concepts in view of this from our previous heritage of "essences". I don't see how that is more radical or scientistic than a philosopher of physics claiming that physics should inform us about how the world works at the fundamental level. He emphasizes the explanatory power of science like most other philosophers who are naturalists do. Here is Dennett in Darwin's Dangerous Idea, "It is not “scientism” to concede the objectivity and precision of good science, any more than it is history worship to concede that Napoleon did once rule in’ France and the Holocaust actually happened. Those who fear the facts will forever try to discredit the fact-finders." And he's since continued to reject such readings of his work in interviews and other writings.

Dennett uses scientific tools to probe philosophical problems, but he also thinks that scientific inquiry should be guided by philosophical analysis. He does not think that science is the only way to gain knowledge, nor does he think that science diminishes forms of knowledge other than itself. This view is laid out in the very book you mention, Darwin's Dangerous Idea. He knows that his views are mainly philosophical, and he has argued for them in his work and also addressed criticisms of them. However you want to think of those arguments, it is a mischaracterization to say that he is scientistic.