Yes, I am aware of the rumors that Ansu Fati is for sale.
There is nothing shown by Ansu Fati that makes Xavi have to make him a core player who is included in the starting eleven in every Barca match.
If Barcelona think that Fati cannot return to his best playing form, sell him and buy another striker as I have stated above.
Lewandowski is physically good so his role this season has really helped Xavi in the title fight with Real Madrid. Very different from the attacker listed in the Barcelona squad.
Ansu Fati also often experiences injuries so his name doesn't appear like Gavi and Pedri.
Reportedly Jorge Mendes pushed Barcelona management to release Ansu Fati because there was interest from a club from the English Premiere League for his client. However, Ansu Fati is a valuable asset for Barca even though he doesn't seem to be able to show good performance. I think that in one or two seasons his performance will be more mature, considering that currently Fati is only 20 years old. I don't think the number of goals can be the main benchmark for Wenger because Barca maximizes Lewandowski role as their pure striker.
Apart from these rumors, it is possible that Barcelona will release their winger this summer. Thus Barca can bring in players who are more mature to get better squad depth, so they can defend the championship trophy next season, if they don't want to be taken over by Real Madrid.