"Every single thing he's done is exploit a loophole, to remain free from a custodial sentence whether in Britain, Sweden or the U.S..."
That turns out not to be the case.
Assange waited in Sweden at the request of the authorities until it seemed they had lost interest. Then he returned to the UK, at which point the Swedes immediately issued a warrant for his arrest. (Still without preferring any charges). He gave himself up to the police and went to court. When it seemed that he would be sent back to Sweden, he sought political asylum.
If he had not done so, his life would likely have been over - one way or another. As you very well know, the US government has not the slightest interest in any law - from the UN Charter to the US Constitution itself. As you very well know, the US government has lawlessly killed literally millions of people who had done nothing to deserve any punishment, let alone death. They would kill Assange as carelessly as they would tread on an ant.
But the most important fact is that Assange has done nothing either wrong or illegal. The leaks he facilitated were an act of great selflessness and bravery. He is not a US or UK citizen, so he cannot have committed treason against those governments.