Thing about going back to the start is that 'hopefully' when you do change the manager - what the new one inherits is better than what the previous one did and he gets the best/more out of those players.
He may well turn results around etc, he has done it here before last season and did it both seasons at saints, but for a team that wants to push on and finally win something - then that in itself is damming, 4 consecutive seasons he would have had a terrible run of form before turning that form around, which is enough to effectively kill you in the cups and for doing anything except the 6/7th placed trophy in a season, the phrase 'just good enough to get you beat' springs to mind.
Could argue about the changing managers thing that basically every single club is doing the same thing these days, Arsenal aside, United went through 3 in 4 seasons after Ferguson, Liverpool, spurs, also have been changing before finally settling on the one they seem to think is the real deal for the club (spurs obviously is, the rs 'looks' to be), Chelsea have it as their entire model to change the coach every couple of seasons at most as well.