Yes, the proposition you presented is indeed utter nonsense. But it's not what Dennett, the quoted author, said. You didn't fully understand his statement. He is addressing what is actually the fundamental premise of Intelligent Design: that natural processes absolutely cannot account for certain phenomena (and for that specific reason evolution cannot be the explanation for such phenomena). That's the claim of the ID advocates. That is the proposition which they must somehow demonstrate, before it becomes reasonable to speculate about non-natural processes, such as an "intelligent designer."
You just restated the same thing. "that natural processes absolutely cannot account for certain phenomena" - You are claiming the ID hypothesis is only possible after one proves all other hypotheses are not true. That is absurd.
The "natural process" or evolution cannot explain IC so the ID hypothesis is very much valid. Using that logic ID advocates can merely say "the fundamental premise of evolution: that intelligent design processes absolutely cannot account for certain phenomena (and for that pecific reason ID cannot be the explanation for such phenomena)"
The double-edge sword strikes again