Is having "more experience and being in his prime years" enough to take a player who will probably get you better immediate results (there is no guarantee for that though as we've seen with some other "proven" players we've bought) but will very likely (but not surely) turn out to be an inferior player longterm (which is what should be considered when rebuilding)? Or do we take a risk with another younger player and add him to the mix of youngsters already at the club? Soumare has played around 80 games in Ligue 1 so he has more top level experience than Ilaix, Puig, Nico and Pedri but he's probably still a few years away from being ready as a starter for a top team (unless we push him which you dislike).
The only one I'd push out is Busi. For a simple reason I don't want to see him as a starter anymore and I think the only way he's not a starter is if he's not here. It won't happen though so I'm counting on him being here next season and still limiting us on the pitch even if we'll make some improvements in other parts of the team.
You are getting way too much into specific and names here and not in the main argument IMO. I have to admit I don't watch football in other leagues so much to compare the names but I will be specifics about "how" as an approach.
There are few arguments here:
1-Going all in about La Masia: IMO it is a disaster waiting to happen, it is bad for both long and short term. I think there is a reason most winning teams have median age south of 25, very rare for young teams to be capable of winning anything.
More important, most of those young players have grown within a need of veteran presence. Players who are older and more experienced with them. Those 2 qualities (age and experience) are important, even if the young player is a strong character or even have 5 years of experience due to playing since very young age.
Even with B teams, which are essentially a youth team, it is important to get few players for them 23+. In first team you need some other level of veterans and not 23/24 years old players.
And right now we just have too many, who are both inexperience and still very young and raw. Pedri/Araujo/Mingueza/Illaix/Puig were all playing in lower division football last year (except few games here and there) Dest has played only 1 season in Ajax team before joining us, Fati essentially playing 1 year of professional football.
The oldest of those folks is Arajuo at 22 years of age.
We will also add Emerson & Eric Garcia next year.
And we have the likes of Nico/Balde and maybe even Ramos Mingo waiting for their chance.
Nah, that won't work, even for rebuilding.
2-Signing players who are a bit older rather than other young players, and financial implications:
First, we are going to pay to sign players in the market, if we agree that we just can't survive with La Masia, then we agree that we will have to pay to get help from outside,
How we are going to get that money, and how much is another argument. Could be new debt or selling club assets, could be just limited budget, or a budget based on selling players. But there will be new signings coming to the club.
Older players usually cost less, due to potential, again I think we can agree with that.
So, with limited budget, and many youngsters already in the team (and maybe one or two young additions, I am not ruling them out completely ) It is worth it to use those resources to best improve current squad, and the necessary environment for their development (again, having proper older players to help them)
You argue that Soumare for example can reach a higher level than Jordan, but OTOH I see players like Rakitic or Modric signing at same age, while players like Cesc or Arthur who were really young and were failures.
Is Soumare an elite talent, a guy you get believing he will be top 5 in his position for half decade at least? If that is the case then he is worth the extra money if we have it, if he doesn't then we are beggars and can't choose to pay extra fee, and we have a bigger need for veterans.
I would also add since you don't like our own veterans, and want them to leave, I wonder what is the alternative? get full youth?