I consider the first observations in your post as obviously devoid of merit. As for the numbered points:
1. total lack of urgency is just shown by delays, and the prior calls by Knox to Filomena without collecting information herself are something which we may also consider a form of "delay", because in fact all her calls and phone conversations with Filomena are slowing down events. They are triggering the coming back and discovery of body by Filomena, but they are also slowing it down. She calls, but she does not provide informations. She delays her own discovery, she waits to speak to Sollecito 'over breakfast' about 'strange events', search and conveying of information is blocked, everything is slowed down.
2. this observation is contorted and unintellegible (negative statement? "the absence of reliable evidence that they were 'caught' "?). I can hardly see a meaning in it. They don't need to be "caught" doing something, I don't see this as a logical requirement in any theory.
3. The "no obligation" = "no failure" is a false equivalence and it's not the first time I see your side bringing it up. The question is about credibility not about obligation. There isn't an explanation for that delay. If you find out something alarming, you are asked to call the police, you agree it's alarming and say ok but then you don't call the police, it does not look a very straightforward behaviour. On the other hand, if two people are guilty, it's obvious they may have some fears and hesitation - for a hundered possible reasons - in the moments before they decide to dial the police number.
And I also think it's obvious that Knox would try to have another roommate there, to involve a co-founder of the body or seek a kind mediation, because this is what she tried to do with Filomena all the time throught her phone calls, her downplaying the loced door etc. This girl thinks that sending a letter to judges, explaining that she doesen't attend the trial because they may found her guilty and that they may be like blindfolded folks fooled by smoke and mirrors, may benefit her. It's narcissistic and megalomaniac, but a person with this perception and attitude - that is, a manipulative person - may well think that by having another roommate there her situation could be made look more favourable.