Talking about Messi, Barcelona is trying to bring him back to Camp Nou next season, if Barcelona succeed in bringing in Messi, it is very likely that Lewandowski number of goals will increase.
There have been plenty of problems within the Barcelona team this season. And so Lewandowski could not show his best performance. Although he is La Liga's top scorer, his performances have not been very consistent. If Xavi can completely stabilize the Barcelona team next season, I think Lewandowski will be able to score more goals. Lewa has this capability. He scored a lot of goals with Bayern Munich. He scored more than 30 goals in most seasons with Munich.