Here are a few things that need to be said:
Weeks in the AP and weeks in the Top Five are two of several logical measures. Others are all time wins, all time winning percentage, undefeated seasons, national championships, conference championships, All Americans and the record in head to head match ups with other helmet schools.
I have crunched all of these numbers many times over the last forty years and they always come up the same. From left to right, west to east, the helmet schools are: USC, Texas, OU, Nebraska, Notre Dame, Michigan, Ohio State, Alabama and Penn State.
You can pluck one of more of the statistical categories away from the others to contend that one or more of those schools do not belong. For example, in this "blue blood" data set, it looks like Penn State doesn't belong. But with all things taken into consideration, they do. All nine schools do.
There has also been talk for years about how this school is slipping out and that school is knocking on the door. Sure it could happen, over the course of several decades if one school continues to slide and another school continues to climb, but statistically there is no way it could happen as quickly as many people seem to imagine it would and feasibly it is very hard to imagine one school sustaining a downward spiral and another school sustaining an upward spiral for long enough to make it happen.
The helmet schools are proud. They will go through bad eras and bad coaches just like everybody else but generally each one of them rebounds and is oftentimes able to sustain the crest even longer than the non-helmet schools because their HC jobs are destination jobs whereas the HC jobs at other non-helmet schools are stepping stones.