I don't think the coach will have a big impact as long as the players stay the same. The condition of the players is very important for Barcelona. If they transfer players who cannot adapt to La Liga, they cannot bring success to the team. Robert Lewandowski still could not show his performance in Bayern Munich. They definitely have to reinforce the midfield. Likewise, they have problems in the defensive zone. The coach should follow these. I don't think it will make a big difference if it starts a new year with the same players.
Barcelona has now entrusted their team to Hansi Flick, Hansi Flick who is indeed an experienced coach is certainly the hope for fans to see Barcelona can compete in La Liga and the Champions League again next season, but as you said, of course a great coach must also get support with good players, indeed we this season saw Alonso do wonders by bringing Leverkusen to victory with makeshift players as well as Girona in La Liga, but I think that is of course very rare and maybe we won't see it happen in Barcelona anytime soon, Hansi Flick, as we know if he previously relied on a lot of star players in the Bayern Munich squad to make it easier for him to achieve Bayern Munich success.
But at this time, of course, we can't expect much from Barcelona to be able to bring in many star players like Munich did before, currently Barcelona is experiencing a downturn in its finances so I think it will be very difficult for Hansi Flick to get support and a big budget from Barcelona because they lack money, unless Barcelona wants to sell Lamine Yamal which is currently being targeted by PSG at a very high price.