No this is not how a reasoning works.
The reasoning works starting from collecting the evidence, that is collect the findings which contain information.
(does not start with a series of answers to the point that appear blank to you, which you frame subjectively and arbitrarily).
When I say information, I mean that findings need to be considered as for their logical value, which includes always weighing the plausibility and probability of the alternative theory. So that a conclusion may well derive from the absence of plausible alternative.
The assumption that there is no evidence o Knox in the room is also false. The fact that she is a female -to start with - would explain the impossibility to find her DNA on the victim's body or on spots where there is Meredith's blood.
The fact that Guede's DNA evidence is minimal, and of the same magnitude and quality of Sollecito's DNA, should be acknowledged by any honest person.
The fact that there can be murder where no DNA of the stabber is found - especially if there are multiple perpetrators - shold also be acknowledged as normal.
The fact that there is Knox's lamp inside the room is evidence of her on the murder scene, and the fact that her blood is found in suspicious circumstances and her DNA is found on blood spots of the victim and on multiple luminol stains mixed with the victim's DNA, even in areas of the house where Knox was not supposed to leave DNA, is also evidence of Knox on the scene of crime.
The fact that there are luminol stains and footprints linkable to Knox, because of their shape, location, and peculiarities (not in trail), should also be considered, at least potentially, as physical evidence of the presence of Knox on the murder scene.
These are example of things that should be assumed when you start looking objectively and honestly. Stating a condition that "there must be physical evidence of Knox inside that room", is prejudice. It's bias.