This argument is flawed.
England need an English manager. I hate it when foreign coaches are in charge of any country. Surely the whole point in international competition is that the entire set up is from that country?
Due to lack of opportunities in recent years, there are very few viable English candidates for the England job.
Finally because of the length of service that Fergie and Wenger have given to their clubs, coupled with the fact that other competitive clubs during this era have tended to go down the foreign route, has meant limited opportunities. For all the will in the world no manager is going to be challenging for the title with the likes of West Ham or Portsmouth, unless they suddenly get a sugar daddy.
Sadly for Redknapp he blew his chance at being competitive (I don't seriously believe we should have a shout at the title either to be honest) among the big boys when he got fired from us because he could do the best possible job anyone could do at QPR, and realistically they aren't going to get into the top six.
As Redknapp stated himself, the role of a manager is often greatly exaggerated. I have little doubt that if Redknapp was in charge of Emirates Marketing Project or Chelsea and they kept him in charge for at least 3 seasons he would win trophies and almost certainly the title also. Likewise if Mourinho (the best manager in the world in my opinion) took over Palace and wasn't allowed to bring in any new players, they'd get relegated.