Arthur is a lot more mobile than Pjanic, can escape pressure better and actually make something of a challenge running back, but they look far apart in terms of that final pass.
It could be unfamiliarity for now but the passes he made forward were not impressive.
To be fair Pjanic was only sideways or backwards passing towards the end too. Last year he was brilliant in like the first month, then he was completely drained and was rather poor the rest of the season.
That backwards pass in the third minute was ridiculous. He had at least four runners ahead of him on the counter, and instead he turned around and passed it back to Danilo.
He can't defend or attack but is good at holding onto the ball when under pressure. That's something nice to have when you have a functioning team that can do both defending and attacking. When you can't do either, you need guys in the most important area of the pitch to be able to do at least one of them.