I agree with you that Barcelona management should have allowed Xavi to remain as their head coach since he managed to win the La Liga title in his second year at Barcelona. Barcelona is a good club that is known for winning trophies, but since their financial situation changed, Barcelona has found it difficult to play competitively and win trophies. A coach can perform well at Barcelona only when they fix their financial problems so that the coach can be able to buy the players he needs in his squad. Flick will not turn things around at Barcelona because Barcelona needs money to overhaul their squad.
I also agree with you. I think management's decision to fire Xavi because he failed to win La Liga this season was a very bad decision. I even think maybe this dismissal has something to do with the bad relationship between Xavi and the current Barcelona president. I agree with you that if Barcelona doesn't fix their financial problems then Flick won't be able to do anything to improve the team either. It is very difficult to find a manager like Alonso who can impress with an average squad. The club management should have retained Xavi because he succeeded in making Barcelona finish in second place this season.