Joshua has consistently fought better opponents than fury, all through his career. He's fought three world champions, fury's fought two. Klitschko, who didn't want to fight, and wilder, who can't fight, yet he knocked 'untouchable' fury, max's words, over twice. When joshua fought klitschko, they both went at it in a really good, exciting fight, in which joshua took a really good shot, went down, got back up and knocked klitschko over to stop the fight.
Just to give a few names that joshua has beaten, who had also fought for world titles before joshua fought them, in no particular order,