I think, Barcelona new manager will going to do perfectly well next season but Barcelona management need to invite some new potential players in this season so that they will not going to experience what they experienced from the beginning of the la Liga league tournament, that made them not to win the title. Robert Lewandowskii is getting older which many people can feel it from his performance, which the new manager need to look into it and bring in new young striker that can handle his position very well next season to bring glory to the name of the new manager next season. Base on the plan of Barcelona in this summer season, I think they will use it well to ensure they will be able to win champion league title and la Liga league title like what Real Madrid did this season, because Real Madrid prepared well to make it happened in reality to win two titles in a season.
Hansi Flick is indeed an experienced coach, but it will be difficult for Hansi Flick to build on Barcelona's declining performance, especially without strong support from management to add quality players to the Barcelona squad next season.
And on the other hand, what Real Madrid has achieved this season and seeing how they have built their squad which looks much stronger, of course makes it even more burdensome for Barcelona to be able to compete with them.
I think realistically next season Barcelona will not be able to compete fiercely with Real Madrid in the race for the title, Hansi Flick needs time to adapt to building this team.