Unlike last season, Arsenal doesn't have only Manchester City to fight for the league, they also have Liverpool and Aston Villa.
Aston Villa might be the least strongest of them all, but they have shown this season that it has what it takes to be among the title contenders.
Manchester City is ahead of Arsenal in 3rd position, 2 points behind Aston Villa, and 5 points behind Liverpool. Manchester City has a game in hand and a win in that game would take them to second position, just 2 points behind Liverpool while Liverpool would lose their highest goal scorer to his national team for the AFCON competition. While Manchester City trio of De Bruyne, Doku and Halland would be available.
Arsenal may not be able to make it to winning the premier league title this season because the competition now is even tough and the contenders are getting even more than it was last season, last season it was more like they had only Manchester city as their biggest threat from winning the premier league but this season it's more.
Aston villas form this season has been really outstanding with their performance as compared to last season they at some point want to dare to be at the top of the table and possibly aim to winning the trophy, Liverpool currently looks very promising with the trophy this season but like you have rightly stated, they will be suffering some set back during the AFCON as their highest goal scorer will be absent but it doesn't mean that wouldn't be able to win games but the challenge will be with the fact that they will have only few goals to their wins.