Arsenal have not yet secured anything for themselves, just like Aston Villa, and it is too early to say that Arsenal has more chances than Aston Villa, besides, Tottenham is quite good this season, so for these three the whole fight is ahead. Arsenal is prone to not very good series, they can lose several matches in a row against not the strongest teams, if they repeat this again before the end of the season, they may even be left without the Champions League zone.
Actually, the top 5 teams still have a chance to secure themselves in the UCL zone because they have a narrow point difference, only the teams are able to maintain their consistency otherwise they will lose that place. Arsenal sometimes appear impressive but sometimes also appear less impressive and are still prone to losing when facing average teams so that if Arsenal is not able to be consistent then they will lose their place in the UCL. The same thing also happens to Aston Villa and Tottenham Hotspur who are still not very impressive at all. the match they are facing. Meanwhile, Man City and Liverpool are still quite impressive and are still on the winning track.
Though Aston Villa look strong and formidable now, would the able be to sustain their present form till the end of the season so as to clinch a UCL spot? I don't think so, I am tipping Tottenham to qualify for the last spot, Arsenal though not a sure title contenders yet has the capability to clinch a top 4 spot, meanwhile the title race is between Liverpool and Man City for now though the overall distance in term of points between those top 5 is very close and narrow as you rightly said, however the more formidable team has the quality in terms of players and the depth to remain consistent in term of performance till the end of the league unlike Arsenal, Aston Villa and Tottenham.