There was some pretty good research in the book 'Soccernomics' about how little impact Managers actually have on results over a long enough period of time (i.e. more than 6 games).
The factor which best determines results and league position is wages. Throughout the last 6 managers (going back to Jol) we have been about 5th - 6th highest wage payers and guess what? We've, on average, finished about 5th or 6th. This is also true of how the final PL table looks; this season the only abnormalities is that Southampton are a few places higher than they have a right to be and QPR are a good few places lower than they ought to be. In fact the years we did finish 4th were years when Liverpool (2010) and Chelsea (2012) underperformed. Last year was an opportunity as Man Utd underperformed but that said Liverpool, Arsenal, Chelsea and Emirates Marketing Project performed to their respective 'par' levels and so finished 1-4.
Based on this research until we start paying much higher wages (which I don't neccessarilly believe we should do) we are likely to always finish around 5th or 6th and will record inconsistent results and performances but will win far more than we lose.