Arsenal's performance has suddenly deteriorated. We saw this last season as well. Despite performing brilliantly throughout the season, Arsenal team failed to win the title due to poor performances and dropping points in the last few matches. Arsenal's situation is similar this season. They have won only one of their last 5 matches. And they have lost points in the last three matches. It is not possible to become Premier League champions with such erratic performances.
It is not the first time that Arsenal decreased their performance suddenly in the middle of the season. This already happens many times in previous seasons, Arsenal often played badly when the first season is almost over or the season is already in second half. In the past, I guessed this was because Arsenal has a bad squad depth. But this season, Arsenal looks to have good squad depth but they still experienced it. So, I don't know what's happening with them. 
Aston Villa team is playing very well. However, I don't think this team deserves to win the Premier League title right now. Second place in the table is now against Aston Villa with 42 points from 20 matches. However, there is a strong possibility that this group will lose the truck and fall behind at any time. Villa players did not play well against Sheffield United and Manchester United. If they play well in these two matches, the top spot in the table would be occupied by Villa.
Every team has the right to win the title, including Aston Villa.But if we consider the squad of Aston Villa, I am also not sure that they will win the title this season. I think the most realistic target for Aston Villa is to finish in the top 4 of UCL standings (UCL zone).