There is a lack of depth. We have Pedri, De Jong and Roberto (who we'll probably see at RB again several times) as CM options. It's clear Koeman doesn't count on Puig. Gavi will be Pedri's sub.
But in context:
On the midfield as a whole Busquets, Pedri or de Jong barely missed or will miss one game when they are fit.
Roberto has also mostly played when fit, although sometimes at RB you are correct.
Koeman has experimented a lot and seemingly prefer, to play with only two midfielders.
I think Gavi should get a lot of playing time against adults, and I think his place right now is as the fifth choice in a midfield that sometimes only consists of two. Maybe Koeman even rates Demir ahead of him still, too.
The natural thing would be for him to start at Barcelona B and play regularly there while being called up to sit on the bench for A sometimes too.
I also think that Barcelona have Puig and Collado already on the payroll, who cannot play at Barcelona B or anywhere else, who have some experience of playing against adults and whom the club should want to play if only to get a better deal later, but that's a bit beside the point.
