Moriba is younger and with much higher ceilling so betting on him is more logical (and he shouldn't be promoted to the first team full time until we're sure we can give him enough regular minutes either).
Different players. Moriba cannot play as a holding CM, while OB can. Barca B plays 433 (OB may play as CDM, while JO a CM, which leaves one spot for either Nico/ IM); thus, OB may hurt IM if he stays at Barca B because of how the team is playing.
And I'd say from what he has shown so far Collado deserves a first team opportunity more than Oriol as well but he'll probably never get one either.
Totally, and I have said that several times. Collado's time is up, and should leave Barca B. However, we have Pedri, Griezmann, Trincao, Dembele who could play either as a RW/ CAM.
Also don't know why you put that much importance for him to just train with the first team even if he'd never play. He's 22 and at this point of his career should play regularly at his current level which is much closer to Barca B/Segunda B than our first team/La Liga.
You have said that he is not good enough. Why would keep at Barca B? If he plays that means we are taking away minutes from other young players, and if he does not, would not it be better to have him with the first team? We need someone of a similar profile (we have been using more or less three players in two positions, FDJ, MP, and Busquets) Best-case scenario, he becomes good enough to play every now and then, worst-case scenario, does not play one minute, which should not hurt either party.
How would him staying hurt other players? If he stays he'd accept to be a backup and only play to give rest to younger players or if we'd have more injuries. As explained before we don't have much depth in Barca B due to poor squad planning, longterm injuries and players like Mingueza and possibly Ilaix being called up to the first team more than expected.
CBs: Comas, Mingo, Marmol, and Marsa
CDM/ CMs: Orellana, Moriba, Nico, Lucas de Vega, and Collado.
You think that promoting him and not playing him is bad because? he is going/ should leave in 6 months either way. We may as well give him the opportunity while we can because we do not have enough players in his position.