Arthur may not have had the best time at Barca so far (mostly due to injury) but he’s still a very talented player and closest thing I’ve seen to Iniesta stylistically in this day and age. His ball retention and ability to glide past players is superb. You only need to read this thread to see what Barca fans think of the speculation:
He offers attributes that currently none of our players have. He’s also only 23, so has plenty of upside with resale value even in the event the transfer went awry. If he can get over some of his recent injury woes, he’d be a great acquisition. In comparison, Pjanic is nearly 30 and we’ve probably seen the best of him. His role in the team is also already covered with Bentancur (who offers more legs too) so he’s not crucial anymore.