in the remaining maths Manchester City should get itself closer and they had to decrease the gap while you think they can even have easier games comparing to Arsenal but still, there is more chance for Arsenal to take a lead.
Meanwhile, Arsenal are getting worse after a 0-3 win over Fulham. They have a five-point gap with Man CIty and sixteen points with Man United. For Man City five points is not too far away with twelve league games remaining. So Man City have big chance to overtake Arsenal, if they make a mistake in the remaining games.
Midfield players are just like the engine of a car, There are kinds of players that their presence mean so much for a team, and in reality it does affect the club and I think this was the case for Manchester united during their game with Southampton and why they didn't do well as expected in their game and Casmero is that kind of player to United.
I think Man United's best player in the draw against Southampton was De Gea. He works hard, his reflexes are also very good. A draw is not bad with ten players, but they are getting farther and farther away from the EPL champions.