If we talk about tactics, of course it will be different and the difference will probably seem quite large. I think Hansi Flick is much more reliable than Xavi and everything will change as long as no problems come. Maybe Barcelona should be able to strengthen their players' physical strength so that they don't get injured as often.
I am very sure that if most of Barcelona's players can avoid injury then they will be much calmer in navigating the competition next season and at least they should not be outside the top four in Hansi Flick's debut as coach. However, if we talk about competing with Real Madrid, it will still be quite far away and it will be difficult for Barcelona to match it.
Xavi has proven his capacity and he has given the title of La Liga and the Spanish Super Cup to Barcelona while the team is down with financial problems. I think it is not appropriate to conclude that Flick is better than Xavi. This season Xavi can also be said to have worked quite well, but he did not get full support because of some things that made internal problems even more tapered. Flick is also a great coach but able to prove that he will be better than Xavi and in my opinion all of that will not be easy.
It's too soon to say if Flick can perform better than Xavi or not because we can't forget Flick had a bad performance in Germany and some people believe this coach couldn't be a good option for a team like Barcelona because Barcelona can have much better coaches instead of Flick in their team.
Regardless of that, Flick made his first decision in Barcelona, and as this first decision, he wanted to expect the contract of their captain Sergi Roberto.
When Xavi was working there, Sergi Roberto was even close to leaving Barcelona but since his contract was about to end, Flick asked the team to extend his contract for a longer time.

Completely agree with you on this . People were too quick to judge whether he was better than Xavi simply because he won a lot of trophies with Bayern Munich during its peak period but flick's situation is kinda different compared to the when he was winning treble winners. Xavi was also emphasizing extending Sergei's deal caused by he was one of very important player owned by barcelona. I believe Xavi also stated that he preferred certain players to stay in the club even longer considering they are very good.
Sergi remained a part of Xavi's strategy, but Laporta dismissed him from the club. The primary issue is that Flick will not have much money to work on it. I recall he had so many wonderful players when he won the treble with Bayern Munich.
Things will be drastically different here, since flick must begin from scratch. Laporta did not initially provide him with a large sum of money. He must be making his own decisions on what is best for the club with so many limitations that exists since barcleona is not good financially.