Xavi was never selfish and Xavi was what Barcelona needed truly in order to be able to start competing with other elites of Europe back, he was fine with unsettling the likes of all his old team mates like Jordi Alba, Gerard Pique and Sergio Busquets, so what matters or why should Ansu Fati get an easy let off, Ansu Fati has been projected to be face of the club, but he can't live up too the pressure with everyone not letting him breathe and him being out injured, so Xavi is gotta reintegrate Fati back into the squad but slowly without taking out the new players that have been working their asses all months long while Fati was struggling with injuries and match fitness, there is no automatic slot for any player and Ansu Fati shouldn't get any special treatment, but he's considered as the future face of the club, so he's also got to prove that he's willing to make certain uncomfortable sacrifices too.
Ansu Fati is still quite young for now and he has a much better future ahead when his performances get better. Loaning Ansu Fati to another club is much more relevant because he will get far more playing minutes there, compared to staying at Barcelona in conditions like these. I believe Xavi has good plans for Ansu Fati in the long term and they are in line with the project he is developing at Barcelona. Xavi also hopes for an ideal squad to compete with other clubs in Europe and especially in the Champions League where in the previous seasons they had difficulty keeping up with other clubs.
Let's see how Ansu Fati can show his skills at Brighton so that when the loan period ends he will be called up again in the Barcelona first team. Now Ansu Fati's future is in his own hands depending on how he can give his best on the pitch and even though many people doubt it. Ansu Fati was once projected as a replacement for Lionel messi but so far it has far exceeded expectations, perhaps also due to the huge burden placed on him because it is still quite easy to accept that responsibility.