"The US" is not a monolith. Guantanamo--both the rapid expansion and ingestion of likely-innocent bystanders and the torture program--was an effort of the Bush-era Defense Department, specifically with high-level support from Donald Rumsfeld and legal cover from the Office of Legal Counsel (John Yoo).
The Assange extradition was a project of the Obama-era Justice Department. It's hard to see any commonalities (in terms of goals or decision-making) at the implementation level, and whatever else you think of Assange, the US's extradition requests have, essentially, followed both international norms and American and international law.
You can try to see some sort of historical through-line here about American imperialism (and you might be right), but, as with my above analogy, that's like saying "the Star of David analogy is pertinent because it relates to the abuse of government power." At a sufficient abstraction that's true, but it still doesn't shed a lot of light.