maybe between Aubameyang and Lewandowski is just for comparison in the team. If only Aubameyang there is nothing competition for the position, that will not good for building the team and the future. Lewandowski is enough experience as an attacker and it's very good for them, especially for that position, and not only as a great goal scorer, he will be good for sharing knowledge with a young players.
It is true that it is more motivating for Aubameyang to compete, but on the other hand they should not forget their weaknesses and only focus on Lewandowski. If that happens then it's useless their attack looks scary, but behind them it's easy to lose goals. Then it will be their next mistake which will add to their burden.
Barcelona still hasn't given up hunting for Lewandowski even though Bayern Munich have rejected the offer submitted by Barcelona three times. Actually, in the Barcelona squad there are already players who are no less good than Lewandowski, Aubameyang has immediately integrated into the Barcelona game since he was brought in from Arsenal, goal after goal was born from his feet and head in his first season. Barcelona does not need to bring in Lewandowski at a high price, especially since he is already 33, they can choose other options to strengthen the team. Raphinha can be brought in from Leeds United, in addition to his young age, his quality is very good, and Raphinha can be used as an investment for Barcelona.