Nebraska is easily an all-time Top 10.
That was a big thing that made the rivalry so special. CU was measuring itself against a super elite.
With that said, I don't think that "Super Elite" is their current reality and it may never be again. Devaney and Osborne had about a 30 year run that was ridiculous (9-3 was literally the worst record they ever delivered for 3 decades). There is so much working against Nebraska these days when everyone is on tv and everyone has state-of-the-art training facilities.
I'm not so sure where Nebraska is at now. Historic top 10 maybe but once you start listing current programs it is really easy to get past Nebraska.