I also don't think sacking the coach will improve the situation for Barcelona. Xavi was a good enough coach. However, Xavi's experience was somewhat lacking. But at the moment, Barcelona boss Joan Laporta should strengthen the financial aspects of Barcelona. Barcelona are in a financial crisis. And we don't know when this crisis will end. It will be difficult for Barcelona to build a strong squad unless the financial crisis is resolved.
We can't claim this now. Let's wait for the seasons starts and see how good the new coach can manage Barcelona. If the new coach can improve Barcelona performance, it is proven that changing the coach makes Barcelona better. But if there is no improvement, we can claim changing the coach is useless. Just don't judge too early, buddy! 
Yes, Barcelona experienced a severe financial crisis. If Laporta can't get the solution, the crisis will last a long time. I don't know what the idea made by Laporta and club management to deal with the financial crisis.
We don't know if Hansi Flick can succeed with Barcelona. But we know Hansi Flick is more experienced than Xavi. Previously he coached big teams like Bayern Munich. Hansi Flick is also experienced in a competitive platform like the Champions League. And that's why fans are expecting Hansi Flick to further improve Barcelona's overall performance. But I would say everything will depend on Barcelona's young players. Young players need to be more diligent. Then maybe we will see a better performance from Barcelona.
Barcelona get a lot of young talent from La Masia. And right now I think the only one who can save Barcelona is La masia. If Barcelona can find talented players from La Masia then Barcelona will not have to spend a lot of money to buy players. And little by little, Barcelona could become stronger again.
Barcelona always get many young talented players from their academy. It is good for the future of the team, they will have many young players for the future of Barcelona. However, this won't work well for the short term goal, they may fail again to win the trophy in the next 1-2 seasons. If Barcelona wants to win the trophy again soon, they must sign experienced players. Sadly, this requires a lot of money!Barcelona have received plenty of young talent from La Masia in the past. This is why Barcelona saved a lot of money. But these young players need 2/3 seasons to experience. Can't expect good performance from young players too soon. I think Barcelona need 2 seasons to transform the current squad into a strong team.