Of course they're a threat. They finished a point behind us last season. But if the assumption that 'ours is weakening' is because Van Persie is going, I think they'll weaken their squad before the transfer window closes too. And I think we'll strengthen.
That Chelsea, Man Utd and Man City will have better squads isn't really news.
We'll know what shape we're in one month from now. What happens to Van Persie, what happens to Theo, who else we sign, whether Jack Wilshere is brought back to life, whether Wenger makes any definite noises about changing the set-up. I guess it's similar with Tottenham with Modric, Adebayor, whether AVB shows any tactical maturity etc.