I won't get surprised if Arsenal throw away their Premier League title chance once again. They have already given the advantage to Manchester City in the standings by losing that game. Arteta has made a big progress with this team since he joined maybe but they are still unable to complete their main target I'm afraid.
Arsenal already missed the chance to win EPL trophy many times, including this time. It makes sense if everyone won't be surprised, it is not only you to see it as a common thing for Arsenal. Anyway, I don't understand why Arsenal should got a lose in a home way against Aston Villa. It is a very bad result, the defeat makes Arsenal drops its position to 2nd place. In the match, Arsenal really dominated the match but they failed to score goals. It is a big question about the quality of Arsenal attackers in scoring goals.
Sure, Arteta has made Arsenal be a very strong team. Unfortunately, Arteta is always unlucky in competing for the title. With the defeat, Man City surely gets the advantage. Moreover, Liverpool also got a lose against a small team at home (vs Crystal Palace). This is also a very strange result, it is unbelievable to see Liverpool losing at home against Crystal Palace.
Aston Villa were of course a tough team to beat on paper but we were still talking about an in-form Arsenal. They got the worst kind of a result. Manchester City have waited for this moment patiently and finally taken the opportunity to take the lead. From now on I started believing in Arsenal and Liverpool less to break Manchester City's title streak.
Aston Villa may a tough team but Arsenal is surely stronger. In theory, Arsenal should win against Aston Villa. But Arsenal defenders played badly, they got 2 conceded goals. I can agree with you that Man City will be difficult to overtake when they are leading the EPL standings.