In my opinion Xavi cannot use or does not know how to use Robert Lewandowski as a goal machine for Barcelona, or indeed Robert Lewandowski's playing style is not very suitable for Barcelona who always rely on tiki taka, we can take the example that Robert Lewandowski is still in Bayern München's uniform, Robert Lewandowski is capable of becoming a goal machine that frightens opposing teams when he is already in the penalty box area, Robert Lewandowski is able to score goals and that is reversed when Robert Lewandowski is at Barcelona even Robert Lewandowski is far from the top scorer candidate for the League this season, even though the League has just started but that It has been seen that Robert Lewandowski did not play freely when he was at Barcelona.
I think it's not because Xavi can't maximize the potential that exists in Robert Lewandowski, but because of the lack of support from other players for Robert Lewandowski to be able to play freely and score goals productively like he was with the former Bayern team.
We also have to look at the team as a whole, Barcelona is not as strong as before and this team wants to be built to be even better after being left behind by its stars in the previous generation, Xavi came to fix that and return Barcelona's performance to its former glory.
So I think it's unfair if we compare Robert Lewandowski's performance at Barcelona now with Robert Lewandowski's performance when he was still with Bayern.