You have touched on a very good point. Lewandowski is an important player but due to his age, he can play well with players who can deliver the ball to him. Because he may not be able to perform as well by running and exerting too much. That is why it is necessary to get a good backup for Robert Lewandowski when he is in the team. Maybe if this happens, Barcelona will be in better places with a player who can benefit from Lewandowski's great experience.
This is about the data and maybe we can see how Lewandowski was able to achieve the overall number of goals last season. Lewandowski's level of play is still quite good because he is still able to adapt to players who are much younger and maybe one of the factors is that Barcelona have a number of players who are able to provide precise passes for him to score goals. If they have additional strength the coach will be much easier to rotate so that Lewandowski can play alternately and we know that Barcelona will face a number of tournaments next season so having a good squad depth can give them a chance to achieve success.
What makes Lewandowski strong despite his age is his ability to be a team player. Not all the strikers have that ability, they can't put back their ego and instead still try to score that goal themselves, but they lack pace and precision and can't do it the same way anymore. Lewandowski in contrast usually never puts himself first at all cost. He plays in spaces in the box that others strikers don't see and he creates space for his colleagues when he knows it is the best course of action to score a goal. His effort to be the first defender on the field is still remarkable. He doesn't shy away from working hard.