If you check the situation very well you will understand that everything is just all about money. If a club has a lot of money, it will be able to buy any kind of coach they want and as well as by quality players to enable them win trophies. But if a club is in financial problems, they will likely not be able to buy any good players or sign good coach and as well they will remain in their financial problem because they will not win trophies that comes with monetary reward.
And that very much you were referring to, PSG had more quality than Barcelona because they were more financially stable and that was why they want and added a whooping $50 million dollars to their portfolio. So dismissing Xavi Hernandez and not serving the financial crisis will not bring any positive results to Barcelona in order to content with Real Madrid this season.
Manchester City showed us with much money they can win Premier League trophies for consecutives season and won UEFA Champion League trophy last season then success become the big four premier league teams since first time acquisition. I think easily become top teams when supporting with much money and Barcelona will be small or mediocre teams one day later if their financial not stable yet and always difficult for registering new player every season behind the financial fair play issues.
Its home work for Hansi Flick with manage player from academy but fans need waiting long term development if want to see their team winning La Liga and Champion league trophies one day later. Barcelona success signing Hansi Flick because he has been free agent manager but not easy for him sign top player because Barcelona just allocated small fund for transferring players.
The case of Manchester City is different because they invested a lot of money in buying quality players and they were also lucky to have a good coach who was able to make good use of the squad in the team to win the the numbers of trophies they have right now I think money played a vital role in giving Manchester City the winning strength.
Right now the chances of Barcelona getting trophies even with the arrival of a new coach Hansi Flick is very slim because they can't have a new coach and expect to have a good season where they will win trophies without adding quality players to their squad. Barcelona is into financial crisis right now they can't afford to bring in some good players unless they promote some young stars from the academy team and they will still need much time to adapt to the team so for now I don't think Barcelona will be able to march Real Madrid who has already solidified the team by adding Mbappe to the squad, I think the president of Barcelona has got a big role to play if really he wants the team to be a team that will challenge other teams for trophies next season.