I would not approach it like that.
When you rebuild a team, you start with an idea for how to play and you shape the team around that. We set to play 4-3-3, and we shape the squad in this direction, based on what we need.
That's what I understand from rebuilding.
I set to play 4-3-3 (because of major benefits), discover the weak points of the system and correct them with new players.
In other words, the job in a rebuild is not to find the system that works best for what you currently have (that's by default thinking short-term as Valverde did with his ancient 4-4-2). It is to develop the team for what you want to play. And besides that, his 4-2-3-1 isn't even working. So, instead of implementing the 4-3-3 we're wasting time playing a 4-2-3-1 which brings us nothing. If anything, it brings us non-stop bench time for one of our most promising midfielders.
But anyway, Koeman is a short term solution. He'll be gone in the summer 90%.
I agree about the idea which you work and develop.
But that cannot happen right now for the following reasons:
All of the old guard should go in order to play a productive 4-3-3 which responds to the needs of modern football. I mean ALL of them.
Because they have gradually accustomed themselves to play a slow, low-intensity, and sterile form of 4-3-3 which you can never shake off.
Basic values (both on and off the pitch) should be taught all over again.
A coach like Xavi would not work for that unless the team is full of youngsters like Puig and Pedri.
I would green-light Xavi becoming manager only when this is the case.
It's obvious we are not there now. 1-2 years are ahead in which one would have to find a way to field Coutinho and Griezman if you cannot sell them.
Koeman has improved the team in the following domains IMO:
(off pitch) reclaimed part of the authority of the coach
(on pitch) Intensity and pressing (OK with the obvious exception of Messi), cohesion and overall structure (team behaving as a unit).
He still has to find a way to improve the following:
Breaking parked buses, Penetrate close to the final third, scoring chances easier
I am not including defensive mistakes here, bcz I think it's a matter of personnel at the back. Not his fault.
I am accusing him of the following:
Personnel selection, and in particular using Busi (and Messi of course, but he cannot do anything about it) and Roberto, and for not playing Puig.
All in all, it's the first time after 2016 that I see some improvements after yearly regress on all domains.
Position in the league is bad, while the Juventus game messed up a really good CL group campaign after a couple of meh group campaigns under EV.
But everyone has to bear in mind how much time changing things needs.
I would rather not win anything this and the next year and then have achieved something, instead of following the Valverde way (sink in all respects with every passing day and hope that squeezing something out of the vets can save the day).
The former points to the future, the latter is clinging on the past.
If Font/Laporta are clever they will give Koeman a year without Messi to continue working, and after that they can go for the coach which will coach the next great Barca side.