Seems like Arteta has gotten the message to get good players to strengthen the squad and that's what he is doing and in a better fashion...I hope this deal to get any of these players doesn't last like that of Viktor Gyökeres...Between these two players who's next to join Viktor Gyökeres? And who is better to be at the squad?
Arsenal are tired of ending the season always as runner up, they now choose to upgrade the squad most likely where they are having problems.
Both midfielders/winger are top class, but it seems Eze might do better due to experience playing in Premier League, it won't mean much to him adapting to the team, while Xavi Simon despite how good he is might want to take some time to resize into Premier League standard, may end up not being better than Eze.
Upgrading the squad is good but another thing is how good they are in handling business when the time comes, because we have situations like this where the team has been upgraded like you said but they can't go 5 games without avoiding defeat not that I'm saying it will happen to Arsenal but it can happen.
Eze has been playing in EPL for long and that doesn't give us the assurance that he will excel with Arsenal that's if they eventually get him, it could be that oppositions have understood how he operates and does his things and he might find it hard to replicate all he has been doing at Palace but Xaxi Simons can come and boom he has gotten that spark on him that defenders can't stop him because is the first time they are playing against him so it goes both ways, so we can't say what is what until then, they are good players but the Gunners should make a positive move first.