Assange has challenged the arrest warrant in Sweden. It was upheld.
He then repeatedly challenged the European Arrest Warrant in the United Kingdom. He lost at every stage, but each of his many legal arguments were heard and considered in extensive detail.
And in doing this, Assange had the assistance of first rate legal advice and advocacy from some of the UK's leading human rights lawyers, and he also had the benefit of having been granted bail in England in the meantime. The extradition was fought by him all the way to the Supreme Court.
Assange has been afforded more opportunities to challenge the warrant for his arrest than almost any other defendant in English legal history. This is hardly "persecution" or a "witch-hunt".