There was a scandal in Sweden too. It’s telling that you Assange conspiracists have been referring to an isolated event in 2007 for over a decade now. There is simply no factual basis for the assertion that it would be easier to snatch Assange from Sweden than from the UK. Especially when you consider what a huge international scandal that would inevitably have caused either government. The idea only makes sense as part of a silly conspiracy theory. If you want sensible people to believe the conspiracy theory, you'll have to do offer more than a largely irrelevant Wikipedia article plus a ton of wild speculation.
The trial is going to be public, as I understand it, so who cares if Amnesty International are there or not? They'll see and hear the same things as anyone else who is there. But anyway, if you are right, this just goes to show that the US can avoid a fully public trial and yet still extradite him, which by your logic gives them even less motive for using extraordinary rendition!