For starters, the teams in 88 and 89 (along with 1990) were expected to take anyone out. Even that 1989 Miami game was winnable at least 2 out of every three times. The fact that the 89 team suffocated a #1 Colorado 21-6 shows how good that team really was. There was never any doubt that we would crush the #1 team that year. When Lou told them that Colorado was living a lie, he meant it.
Were there some games that were closer than they should have been? Yes. Stanford in 1989, Pitt in 1988, and a few others, but in the end, the teams did what they were supposed to do.
Back in those days, you had a handful of truly elite teams, such as ND, Miami, Florida State, Michigan, USC, and a few others.
The teams in 2017-2019 are good, even very good at times, but not elite like the Holtz ear teams were. None of these teams could be realistically expected to take out an Alabama, Clemson, or Ohio State team in its current form. We would have to rely on a lot of divine intervention on our behalf, and some divine wrath directed at the opposing team.
Also, the teams in 2017 didn't play nearly as much of a murderer's row schedule that Holtz's teams did. While these current teams do have some quality wins, I still don't see a signature win that has everyone whooping and hollering in joy.