Puig is definitely better than Arthur for this Barca side, even now. Style and fit matters, and Arthur contributes more to this Setien epidemic of slow play with no real aim and no clear passing lanes to the goal.
Puig, on the other hand, moves the ball rapidly and constantly follows up on his passes. We need a fast tempo which is what Puig provides, as does FDJ in his natural position. This is how we get rid of the gridlock in buildup and continuously produce high flowing offense and good chances.
Him being so small as well helps him have crazy cardio. Probably top 5 cardio in the team after FDJ/Vidal/Semedo/Roberto. Never slows down.