Man City have been building their squad and spending money year after year just so they could compete well in both leagues. You can't really say which team has a better form since City also defeated Arsenal in their last match. We'll see how things go from here but my point remains that 5 points ahead with 11 games left doesn't make the Gunners too far ahead. They could also choke. Remember that they are also competing in the Europa League and that could affect their squad too.
Winning the Premier League will be much more prestigious for them than the Europa League, so I think that they will concentrate all their strength on this championship. I agree 5 points is a significant advantage, but it is realistic to cut it for City, as I am not sure that Arsenal can win all the remaining games without dropping points. This may also apply to City, after all, they still have 11 more rounds to play, during which time a lot can change.
With the remaining matches they will still play, Arsenal's position is not completely secure, so they must really focus and not make mistakes that will cost them a loss in the end. Manchester City is a very strong team, they can wipe out the rest of the game with a win, that's what Arteta should be aware of. Maybe they will also share their focus on the Champions League, but that doesn't mean they will let Arsenal go comfortably in the Premier League.