How is that more appropriate? At all? Like, even a little bit? Why would it be? How do you determine the appropriateness of this? 

 Good lord. How does one get to make etymological findings? Word go in book. Word go in dictionary. You can't prove an opinion one way or another. It was always negative. Slovenly > Ugly/Rubbish > garbage can ("Slut-hole") which was a 19th century term for garbage... all of that can easily be transformed metonymy/synecdoche into how we use it. Indeed the concept of dishevelment is as related to "loose" as anything... and sex tends to make one disheveled. Both terms begin the etymology game a single degree of Kevin Bacon from what we have. And by the way you need to fill in the gap between bitch applying primarily to women rather than dogs to make this leap, which you didn't do there.