Some days ago he was already praised as the new world football player. 4 days later everyone is back with his feet on the ground. Don't judge a player on one match and defiantly don't judge a pleyer on 20 minutes. Marcelo played 70 minutes more than him. If I run with a guy that has played 70 minutes more then it's normal that I'm less exhausted that him.
Still his overall report for his 4 months is POSITIVE. But still he should work on his finishing if he really want a future spot in the starting XI. If you play as Winger for FC Barcelona you need to make assists, what he does, but also you need to be able to make some goals.
I'm sure he keeps working hard and will grow more as a FC Barcelona player. I doubt he will ever have a spot in the starting XI. Players like Pedro, Villa, Messi, Xavi, Iniesta, Busquets, Mascherano you don't bench that easy. Still for the time being he is a very good back up.