If it is the right transfer, I don't look at that person as a 4th, but as a person to share Kante’s time when he needs rest or has a knock. That person could be more valuable to the team and season than just a 4th.
I just read the game thread at Arsenalmania. Most of them predicting a slaughter with Rom getting a hat trick is having the reverse effect on me. I would have been more assured if they unreasonably thought they could win. In their poll 78% picked an outright loss. I do hope Rom destroys them. They want Arteta run out.