I agree with @QuincyAbeyie in that we should see how Ange approaches this second season before rushing to judgment. But if he continues to take the approach of "We are going to play our game and we aren't going to compromise that for anyone" with their high line and high octane style, they will not be a threat to the title. Arteta and Pep have shown that you need to be willing to sacrifice your ego to adapt to the opposition and be flexible in your approach. I think it was Rob Edwards who said it earlier this year but Arsenal can play any style right now and that is such a huge advantage over 38 matches, especially combined with the control we exert over 90% of those matches.
Thus far, we have seen Ange be very inflexible with his tactics (the Chelsea fiasco comes to mind first and foremost in its naivety) but let's see how he does next year with a full summer to shape the squad. If he continues to be stubborn next year, they won't be anything more than a really tough game for big teams but a non-threat over the course of 38 matches.
I am not worried about United or Chelsea. They should be very concerned about falling further back from the likes of Villa and Spurs if they don't absolutely ace this summer but to me, 4th - 7th will be their ceiling even if they have 10/10 summers. I'd be very concerned about the underlying numbers if I am a United fan as they have vastly over performed all season and that chicken may come home to roost next year.