I think you have to view Wenger's competitiveness in relation to that stadium move they made. Arsenal found it hard to find their feet for years after the switch to the Emirates. Also they had to pay for it and though they were/are competitive on wages they dont spend as much as their peers on fees. The stadium took precedence and towers over all other matters at that club in recent seasons. Even with that though Wenger has them in the CL every season. Outside of SAF here hasn't been a PL manager like him. Throw a cup in every so often and his record is superb.
I'm not ignoring the stadium issue as obviously it placed restraints of them, but I don't think it is excusing Wenger's current
stubbornness*.
Wenger at Highbury was marvellous and the Emirates initially constrained his squad, yet that's less of an issue now as they clearly have money.
Look at the expenditure on Ozil, Sanchez, Mustafi et al. And they can play some marvellous football at times which is a joy to watch as a neutral.
However, that killer instinct for success that he once had seems to have gone or he (and those above him) have become complacent
Stability is fine and don't get me wrong he's been a marvellous manager, I just feel that a little bit more risk and they could be successful again.
Instead, they do not rectify the same ol' problems everyone and his dog can see and that eventually leads to them bottling it later on.
*stubbornness may not be the most suitable word, but it probably best describes how I see it.