If Arthur comes, he probably won't be at Barca's level (starting 11) for at least 2 years.
In those 2 years, we'll see whom we'll get rid off.
Till then:
1. Iniesta will retire
2. we'll see what will happen with Rakitic and Paulinho
3. Alena may improve or fail
4. Coutinho or Dembele may turn as failure
There's no need to hurry and sell players because of unproven Arthur.
You would:
1. move Busi to a CM
2. play Alena as a CM
3. play Samper here
4. buy Arthur
5. play Roberto as a midfielder
The only problem, that besides these 5, we still have: Coutinho, Iniesta, Paulinho, Dembele, Iniesta, Rakitic (Gomes and Denis).
I meant for the coming year, bro. We can't have 9 midfielders for 3 positions, even though they're all good.
So like everyone, I'm trying (looking towards the future) to see what's best for us.
If you read well, you'd see, for Busquets I was talking about the future, explaining why Oriol can't be promoted directly.
Basically it seems we'll buy Arthur anyway, so it's just a matter of who do we get rid of.
(Btw, I'd loan Arthur back until December, at which point Paulinho can be sold) to get this:
DM: Busquets/Samper/*Oriol (B team)
CM: Roberto/Rakitic/Paulinho (December: Arthur)
AM: Coutinho/Iniesta/Aleña