Arsenal looks better because the team's progress continues to move in a positive direction, but whether or not they win at the end of the season is not only determined by the team's performance, there are several factors, one of which is mentality and I think that is a strong reason. they cannot become champions because mentally they are no better than Manchester City.
If you look at the progress they are going through, of course for next season Arsenal's performance can be even better, but winning the Premier League title is not easy, this is the most competitive competition.
I would love to know how you define your concept of mentality that gat you thinking Arsenal has got no winning mentality and so they have been unable to win the premier league title because of that, when Manchester city had some set back last season that they couldn't beat both Arsenal or Chelsea in their first meeting was that perceived like they were loosing their mentality, when they aswell were in the title race to a point where Liverpool and Arsenal were points ahead of them, they still had their mentality intact going by the way you present them to be, so why then is Arsenal different.
All along the journey to the title last season, Arsenal has been at their best and I don't think of they didn't have the mentality they would have been able to have gone as far as they went and were able to become the runner up by a point difference, the only thing I see as the problem Arsenal had was timing and priority, they gave priority to the premier league late and so they didn't get the right timing to maintain their wins enough to give them the edge over Manchester city because at some point when they were at the top of the table, they felt they have got enough points ahead and shifted priority to the champions league awhile.