When he had subbed off he had the most passes on the pitch, and he runs more km per game than Rakitic/Busquets easily too. Created multiple big chances, was playing dagger passes to Messi and co. all night. Incredible player, and impossible to dispossess or force into silly errors.
People talk a lot about how we don't have "off ball movement" from the front 3 or in general. That is correct, however, no one is in a good position to move off ball when they are receiving a pass from the likes of Rakitic who gets the ball, turns, and immediately dumps the pass off. In that situation, the opposition defense hasn't shifted at all, and there isn't any pocket of space for X player to move into. No one has room to move in a static setup.
With Arthur, he carries the ball and draws the defender. That motion causes everyone in the vicinity to move/adjust their position and that is where pockets of space are created for the runners to move into. That's why players look so open off the ball all the time when Messi is on it. It's the same with Arthur, and that is why he is so crucial and unique in our midfield. There's literally not a single other midfielder we have who does this.