Rabiot, well, he is tall, strong and not as technical as classical Barca's midfielders...
Since when is a player 1.88m tall and with a weight of only 71kg considered strong. He is a weakling the same one like Busquets, the only difference is that he is much faster than Busi, but that doesn't say to much since Busi is a tortoise and Busi is 5kg heavier with identical height.
So the only thing Rabiot has is height, nothing else, he is skinny and weak, not technically good enough, not fast, not a fighter on the pitch, so what do you see in him.
He will bring nothing to Barca, he is the french Gomes with a much worse attitude. Rabiot is the definition of an average midfielder. Roberto who is not good enough to be a midfielder for us brings more to the table than this guy.