Xavi may have left a solid legacy at Barcelona but even without all that, I think Hansi Flick will be able to achieve success with Barcelona as long as he has full support from the boss. Hansi Flick is a good coach, and I think Barcelona was very fortunate to be able to sign him to replace Xavi. The only problem that might be the biggest obstacle for Hansi Flick is Barcelona's financial condition which might prevent him from being free to recruit the players he wants.
Yes, Barcelona was very lucky when they managed to get Flick, he is a figure who previously had quite a brilliant reputation. Financial problems are of course an obstacle for him to be able to get new players in the transfer market. However, the current squad is also quite competitive and Flick must be able to manage it well and not completely change the scheme inherent in the Blaugrana, namely tika-taka. Flick must also be able to get support from fans so that it is easy for him to compete with Real Madrid.