Yes, Aubameyang is a good striker, he already proved it in Dortmund, in Arsenal, and in Barcelona.
Although he played for a short time in Barcelona, he can show us that he is a skilled and talented striker. He scored some goals in important matches and become a player who contributed very well. When he was in Arsenal, he becomes the club top scorer, too. No doubt that he is a great striker. Now, he only needs more time to show his contribution in Chelsea, he also needs another striker who can help him to optimize his potential. Sure, Nkunku seems fit with Aubameyang and Chelsea squad.
About Aubameyang leaving Barcelona, I don't think it is a mistake made by Xavi. Xavi knows that they have Lewandowski, it is not necessary to have Aubameyang too. Aubameyang must be unhappy sitting on the bench, he needs time to play regularly. So, to minimize the conflict, Barcelona prefers to sell Aubamayang.
Chelsea reportedly gave a very large value to buy Aubameyang and I think it was a stupid thing for Chelsea to do, Aubameyang has been on the bench for too long, that's the reason I doubt his potential in the future, especially since Chelsea is currently catching up other clubs in the EPL
the transfer market in January will be very busy and Aubameyang's transfer will be one of the most expensive later
There will be a general activity in January because very important football players were showcased in the World Cup. In particular, we saw the high-level performances of the goalkeepers. Livakovic's name has already started to be mentioned with many teams.
As for Aubameyang, this year he has not been able to perform as he wanted. He had a good form in Barcelona, but he can't find enough chances in Chelsea this year. Moreover, the fact that he is 33 years old marks the period when he entered the regression in football. I don't know how effective it will be after that.