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It's a little clearer if you take it year by year.
Oklahoma was good out of the blocks post-WWII, and was a team that could have been named national champs (at 11-0) in 1949.
Starting with the 10-1 1948 team, it had its greatest stretch ever going through the '58 (10-1) season.  107-8-2 over that 11-year stretch.  But the Wilkinson magic faded (not just coincidentally as Bud's former player Darrell Royal really got it going in Austin) and Bud finished 7-3, 3-6-1, 5-5, 8-3, 8-2.  That went through the '63 season.  Bud's successor was long-time assistant poor old Gomer Jones, who went 9-11-1 over two years.  The rest of the '60s were "OK," but just that, with the exception of the overachieving '67 team that was 3 missed FGs against Texas in a 9-7 loss from being undefeated and possibly national champs.  Then seasons of 7-4 and 6-4 closed out the '60s.

Then, in 1970, in the bye week before the RRS, OU installed Texas' wishbone offense (only emphasizing more speed and less power) and ended up with a 7-4-1 season and momentum.  Then they ripped off a great decade, with Barry Switzer taking over from Chuck Fairbanks for the '73 season.  11-1, 11-1, 10-0-1, 11-0, 11-1, 9-2-1, 10-2, 11-1, 11-1, with 2 MNCs in there.  (Bama had a lower winning percentage, but won 3 MNCs, over the same period.)  The '80s were a down-up-down decade.  Subpar recruiting led to a 10-2, 7-4-1, 8-4, 8-4 start.  Then, '85 through '87, they went 33-3 with an MNC in '85 and losing to Miami in the '87 MNC game.  But then a decline at the end, 9-3, Switzer getting forced out, and closing out with 7-4 under Gary Gibbs in '89.  The '90s then made the '60s look like a roaring success story.  8-3, 9-3, 5-4-2, 9-3, 6-6, and Gibbs getting fired.  A 5-5-1 season under Howard Smellsofbourbon, and then the worst 3-year span in the program's history under John Blake, 3-8, 4-8, 5-6.  Bob Stoops' first year, at 7-5, closed out the decade.  2000 brought 13-0 and an NC, and another nice run--albeit with disappointing performances in NC games--from that point through the 2019 season.

So, up at the end of the '40s, down at the end of the '50s carrying into the mid-1960s, a one-year spike, then back to mediocrity for the rest of the decade, then a great decade in the '70s, a good decade in the '80s, a lousy decade in the '90s, a great start to the '00s, and a good run since then.

One of my plans for this off-season was to do a 10-year rolling winning percentage chart for at least all of the helmets (maybe Mandel's Kings and Barons) to look at this in more detail.  Just using decades can be highly misleading because if a team was REALLY good from say 1955-1965 and REALLY bad in the early 1950's and late 1960's then the 50's and 60's are going going to look mediocre when in fact that team wasn't mediocre for those 10 years they were REALLY good in the middle and bad outside of that.  

My premise is that our current helmets all had a good decade in the 1970s and whatever status they had going in was confirmed and strengthened in some cases, and they are still viewed as helmets - Texas, OU, ND, Bama, OSU, UM, USC - those are my Blue Chips (for the moment).

To some degree, I think of this as pertaining to who would be exciting to schedule for my lesser team, and it's all of them.  No matter how bad USC might be, they still carry that panache (for now).  As a fan, I'd be excited to schedule Wisconsin and Penn State and teams of that ilk, but it wouldn't "fee" the same.

Some of this for me of course is because UGA didn't play anyone of note on the road for eons (1965 to about 2005 or so) outside bowls.

I recall the 1980 season for some reason, and even then for UGA to be on TV was notable.  I was trying to listen to radio at night most games.  The UGA -UF game was not shown in Cincinnati because of Kent State playing Akron, I'm serious, but that game ended early and they did switch over at the end.

I think cable is what expanded CFB TV.

Seems like the old College Football Data Warehouse may have had that feature.  Maybe a rolling 25-year average too.

Alas, it is no more!

I can get the data keyed in at least for the Helmets and maybe the semi-helmets.  Once I get it keyed in, I could switch from 10-year rolling winning percentage to 25-year rolling winning percentage pretty easily.  

The main shortcoming to me doing it is that it would be limited to ONLY those schools that I chose to include.  Ie, I'm not keying in every single college football program that ever existed.  I'm just not.  

My thought was to do it for every school that has a case to be a "helmet".  Ie, using Stewart Mandel's Kings, Barons, Knights, and Peasants I'd include every school that had been listed as a King on any of Mandel's lists:

• Alabama (all three lists)
• Florida (3)
• FSU (3)
• Miami (3)
• Michigan (3)
• Notre Dame (3)
• Ohio State (3)
• Oklahoma (3)
• Penn State (3)
• Texas (3)
• USC (3)
• Tennessee (2, 2017 deletion)
• Nebraska (2, 2017 deletion)
• LSU (2, 2012 addition)
• Clemson (1, 2017 addition)

Of the schools included on all three of Mandel's lists (2007, 2012, 2017) I think the three most frequently questioned are the three Florida Schools.  Florida, Florida State, and Miami have been very good for quite some time now but there are still plenty of living fans who can remember when UF, FSU, and Miami were not nationally relevant.  Then there are the four that Mandel added or deleted:

• Tennessee:  I think they are somewhat of a borderline helmet.  They have a lot of great history but this is a REALLY strong group and when you compare Tennessee to the other "Kings" they tend to fall near the bottom in most metrics.  
• Nebraska:  When Mandel took Nebraska off of his list of Helmets in 2017 he said this:  "I’m 41 years old. In my teens, 20s and early-to-mid 30s, you could never have convinced me Nebraska would one day be viewed as anything less than college football royalty. But today’s recruits were not even born the last time the Huskers won even a conference championship, in 1999, much less Tom Osborne’s three national titles in four years from 1994-97."  I'm almost exactly his age and I feel much the same.  Nebraska's run from 1962-2003 under Devaney, Osborne, and Solich was incredible.  For those ~4 decades they were among the top two or three on nearly any metric you could choose to rate programs.  The problem is that they also have a lot of decidedly mediocre performance outside of those ~4 decades and it has been a REALLY long time since Nebraska has looked like a true helmet.  
• LSU:  Their NC this year makes Mandel look pretty smart for including them back in 2017 but I still have my doubts.  LSU isn't up with the rest of this group on most long-term comparisons.  If they keep performing at their current level then they'll be an obvious helmet eventually but if they sink back to mediocrity . . .
• Clemson:  I strongly disagree with this decision.  Clemson has been phenomenal over the past decade or so but their overall history is simply nowhere close to most of the rest of the helmets.  Maybe this is their new normal and they are a helmet but it is also possible that many years from now Clemson fans will still be looking back wishing they could have this back.  We'll see.  

I think I dropped Nebraska into the near helmet group myself inadvertently.  I think USC should be on the fence also, teetering.

The current "Three Kings" are Bama, Clemson, and Ohio State, I think.  Oklahoma could be fourth.  Those three seem to be 1, 2, 3 in some order each preseason, and fairly often post season.

I suspect for most of us if we woke up and learned we signed for an H&A series with any of them, we'd think "Whoa.".

If you signed with USC, you might think "Cool, we'll probably be able to beat them twice and get some luster.".

I think I dropped Nebraska into the near helmet group myself inadvertently.  I think USC should be on the fence also, teetering.

The current "Three Kings" are Bama, Clemson, and Ohio State, I think.  Oklahoma could be fourth.  Those three seem to be 1, 2, 3 in some order each preseason, and fairly often post season.

I suspect for most of us if we woke up and learned we signed for an H&A series with any of them, we'd think "Whoa.".

If you signed with USC, you might think "Cool, we'll probably be able to beat them twice and get some luster.".

That's why I'm pissed that we haven't scheduled a series with the Trojans.  First, we owe them some payback and, second, if we're going to play a series with some lousy-ass southern California team, why don't we make it USC instead of UCLA?

Yeah, I think the Dawgs have a series with Cal or UCLA, I can't even remember and don't care.  Meh.  If we had one with USC I'd remember.

That right there is why they are a helmet.  

If your team beat a 5-7 USC you'd be more excited than if they beat an 8-4 Cal/UCLA.