Alves never shoots anymore, his crossing is useless 90% of the time, and he's only good in boosting our numbers up front. Adriano is a different type of attacker. When I talk about Adriano as the right winger, I mean really as a right winger. Not the fullback/winger thing Alves does. Adriano can play wide, he can defend, he can cut inside, and he can shoot from long distances. As I write this, I am reminded of the Atletico game this season where he scored a beautiful goal with his left foot cutting in from the right. That's exactly what we need there.
Agreed, Alves is just 'boosting our numbers up front' or in other words just helping in ball retention, but as you say, he does not present enough of a direct threat to score or assist. He doesn't have the speed he used to when he would consistently get past the outside of the left back no matter how he was defended. Now some left backs are actually challenging him quite early up the field, unafraid that he'll just run past them. This didn't used to be the case.
Also he's now always being showed to the inside, where he doesn't present any threat at all and where the Barca attack comes to a dead end.
Now if Alves could learn to do what Adriano does and be a shooting threat with his left foot, that means defenders would have to play him more neutrally, and it would also open up the outside to him. He a double threat, he would easily make up for his lost speed and add years to his game. But he hasn't.
That's why I would agree with you and would have liked to see Adriano at right back more often. I'm positive that most opposition teams, especially their left backs, would not have liked that.