I don’t understand, “did not achieve the success he should have.”
What success should he have experienced? The last 4 years of the Mack Brown era, (2010-2013) Texas was 31-20, .589 winning percentage and a losing season in 2010, (5-7). In 4 years, 2017-2020, Tom Herman went 32-20, .640 winning percentage and 4 bowl wins. The .640 winning percentage is the second best since 1987 for Texas. David McWilliams (1987-1991) 31-26, .544.
John Mackovic (1992-1997) 41-28, .592. Charlie Strong (2014-2016) 16-21, .433. Mack Brown has by far the best winning percentage.767, (158-48), but again his last four years were subpar. Charlie Strong was a nightmare and Tom Herman got things back on track and even surpassed Mack Brown’s last 4 years.
While he did not exceed the Texas fans expectations, it is generally accepted that their expectations are unrealistic. Many coaches, including Saban, have not shown an interest in the Texas job due to the unreal expectations of the administration and fans.
I think Tom Herman has the potential to do great things at Nebraska.