Purdue is not a program that will be able to recruit elite 4/5-man classes consistently...that is not unique to them either admittedly...but, it has had to do it three times and is going to do it a 4th...it worked out twice...which is a credit to Painter/Purdue...it definitely did not work out the third time...if it works the fourth time, we will all celebrate the 75% success rate, however, if it fails, we will all lament the 50% success rate.
You can't have sustained success replacing 4 or 5 guys in a class, especially if your premise is as you stated to "get old/stay old", as, three times that has not been the case already and there is going to be a fourth time...aside of programs where they are annually turning guys over (and don't subscribe to that philosophy of get old/stay old (much less proclaim it as Painter/Purdue has)), I don't know of another program, much less elite program, where every 4/5 years they are adding a 4/5 man class that HAS to be the foundation of the program for the following 4 years.