I think progress has been made on some purely football aspects (along the lines of what Horatio said above), but the huge advantage Koeman has over Xavi or any other coach that will stay for long is that Koeman can do the dirty job and then leave.
Reimposing the authority of the coach and principles, cracking the entitled sickening mentality of the Amigos and the dressing room.
Now imagine Xavi (who is a bet anyways in terms of his coaching abilities, but let's assume for the sake of the argument he is the next Pep) walking in the current dressing room with his former mates running the show after years of entitlement and detachment from reality.
Just think yourself if he will be able to change anything.
No rebuild can happen without that cracking, deal with it...
Ernie was a Koeman-type strict coach when he was coaching Olympiacos and would not take shit from anyone.
But in Barca he turned into a scared little mouse that would bend over to Amigos.
Many (most) candidates out there do not cut it for that particular job. Xavi would be a terrible choice to do that.
Not all coaches are good at both, only handful of people have done that successfully.
That's why I say Koeman should stay put until his contract ends, until Messi is gone, until Busi and Pique are retired or relegated to the stands, until possibly Griez/Cou are also either gone or sorted out, and then the rest of the youthful and upcoming core have learned basic values and mentality, and then are set to learn how to coordinate on the pitch.
Then it's the time for Xavi or Poch or Ten Haag or whoever it is to build in terms of football