Well the league is just starting and im not going to write off Lewandowski yet due to his inability to start getting goals at the early stages of the tournament, there are several top flight strikers that are having same difficulties currently but will definitely pick form along the line and even end up scoring braces or hat-tricks in several matches.
Barcelona where very brilliant against Cadiz though they had a tough time in getting the goal at the 1st half of the game but they were very dominant and played like they really wanted to win the game which paid off with a 2-0 win later in the 2nd half, Lewandowski is an experienced attacker he's very good at the goal and gets it at Crucial times i believe that's why Barcelona got him, and sooner than later he'll begin to get the ball in the net.
Yeah Lewandowski performance was bad against Getafe, but in this match against Cadiz, he already good enough by giving an assist. Although we know Benzema is really great striker and he many times score hattrick, but he's not always score a goal in every match. There are many matches he performed poor and no give any contribution.
I think as long as Barcelona win the match, it's already enough.