Not impressed with him last night, but I'm optimistic with his/Barca future. He's playing his first games at Barca and for Brazil squad, just like he played his first games at Gremio: dropping to collect the ball, passing around, doing his turns to keep the ball and build the play, with caution, not risking much, slowly building confidence, and doing things that gives you some glimpses about what he can do.
During 2017 season, he started to play week in week out and doing more and more extraordinary things, like that Libertadores Final, his best performance so far. So I think he's being smart. For both club and country, Arthur doesn't know his teammates well, so he's building confidence by doing simple, but important stuff, like never losing the ball. At Gremio, it worked so well, so he's trying to do the same for Barca & Brazil, playing "safe", until he's fully adapted to both teams.