It seems that Xavi is very satisfied with the striker he currently has, Lewandowski presence has revived Barcelona front line, Xavi still has a stock of quality strikers that he can rely on this season. Barcelona has no problems at all in the defender position, while the midfielder position is already filled with quality players. Gundogan arrival can be a new wall for Barcelona in keeping the central area solid.
Lewandowski was able to answer Xavi's wish by scoring goals in his first season with Barcelona. It is undeniable that Xavi must look for Lewandowski's cover because Ansu Fati, Ferran Torres, Raphinha, Dembele are not pure centre-forwards.
Barcelona's ideal 4-3-3 formation is slightly advantageous if Xavi defends with one centre-forward as a winger can be a goalscorer assisted by a creative midfielder but there are times when Lewandowski gets injured and will turn into a weakness. At least that's what I feel.