Barca are starting to find form with Xavi as their new coach this season. I'm not completely sure that Xavi can't bring any changes to his team because so far I can see that Barca are starting to make things difficult for their opponents in the league. Of course that's good, but the difficulty of scoring goals and winning match is a problem that still exists today.
As much as this paints a good picture for Xavi, Koeman was not a bad coach as far as I know because he came to this club with a well decorated CV.
Koeman is a really good coach his Netherlands national football team was very strong the problem is that he could not influence the team as he needed, the main reason is why he failed to achieve a result.
Xavi is more influencing the team now than Koeman was in his time. If the president of the club doesn't prevent Xavi from doing everything as he wants, then Barça will become great again

Wait, let's evaluate while Xavi is at Barca. Pretty good and little by little can change the course of Barcelona's game. Even though it's not too significant, Xavi seriousness in bringing Barcelona and young players to try even harder already looks good. it's just that in La Liga opponents Barcelona know this El Barca weakness. So Xavi is here to cover the gaps in the gaps that young players have. Small hope, but next season this is still a question mark.
Not even a world class coach like pep guardiola could make a bold changes in current barcelona mess, it takes years to bring back the old unbeatable barcelona , there is too much missing from this club ... a top player like messi , a great leader like puyol, a maestro like iniesta and xavi himself...
so yeah i think xavi is trying to find a huge potential from the academy and of course it cost a lot, it has a huge risk giving too much space for young talent in a competitive league.
In recent days, when comparing to A Madrid and R Sociedad ,Barcelona is really performing well and that needs to be on 5th place. Yes I am not aware of how best Barcelona was, but yes the current coach is really giving out his best to the players I suppose. I am sure , if the players follow him then, he is going bring back Barcelona's earlier performances back.