Halilovic would be already playing in A-team, if we had no Messi. They play the same position and with Messi minutes Halilovic is unlikely to get enough time on pitch to develop further. That is the only reason for his loan, not his abilities.
Adama lacks awareness, but that's the thing that can be learned more easily than ball control and speed - and in those two apects of game he's only second to Messi in whole team including Neymar, Suarez and Iniesta IMO. I don't believe our B-team was good for his development. I heard Eusebio did not talk to some players for months. That's absurd, young talents need guidance.
Rafinha is also the same type of player as Messi but he's much better than Halilovic. Alen overall is nowhere near ready for the first team and even without Messi he would still have a long way to go until he is.
Where is Adama going to learn his awareness? On the first team bench? On the bench of some loan club that doesn't like him because of his lack of awareness? Or at some loan club that lets him start every game despite his faults that he doesn't try to improve?