This ruling is to be expected, as it was only about the extradition, not about guilt. The question to be answered was whether Assange would get a fair trial in the US. An allied western country is never going to go against the US, that would be a significant diplomatic affront.
What Assange did is not so much different than the Pentagon Papers and would center on whether Assange qualifies as a journalist, and how much assistance he gave to whistleblowers. Assange might well win his case -- after a very long legal fight.
My guess is that the US is not particularly interested in the case going to court either. This is mostly about sending a signal to other potential whistleblowers. Even if he wins, he would have lost 20+ years of his life -- counting from his escape to Ecuador to a Supreme Court appeal. The US government wants potential whistleblowers to take notice that your life will be ruined one way or the other.