I am going to jump into this one (may regret it).
I agree with your post.
I think the debate for the best team is between 2019 LSU and 2020 Alabama although perhaps 2022-2023 Georgia should enter the conversation.
1995 Nebraska would have no clue on how to cover modern offenses. Keep in mind that between 1995 and today you had multiple new offenses such as the Wild Hog, Spread, Hurry-up, Air Raid, etc. implemented and many of these ideas are present in 2019 LSU and 2020 Alabama. These offenses vastly changed the game and caused dramatic shifts on defense strategy and how defenses should play. 1995 Nebraska's defensive coaching staff would have 0 clue how to cover these offenses in a matchup. I also think secondaries, overall, were not as strong as then. I watched 1998 Tennessee vs. Florida and 1995 Tennessee vs. Alabama recently. All were top 10 teams in that era with solid defenses and what was considered solid secondaries. All four would have been torched by modern offenses and schemes.
Look at QB stats. QBs today are far more dominant than Elite QBs of that era when it comes to TD-INT ratio, Completion ratio, etc. Athletes overall between 1990 and 2000s got bigger. I do think some of the athletes have regressed a little in modern era but not enough to where I cannot say that athletes in 2019 are overall faster, bigger, and more talented than most players from 1995.
I do think Nebraska might could win some physical matchups but I just don't see how schematically they could have matched up with a modern offense unless they all of a sudden were able to download all the info of how the game changes like Neo does in the Matrix with Martial Arts.
To take a war comparison. It is like matching up the USA navy in 1945 vs. a modern USA naval fleet. It would get ugly quickly. The game has changed that much.
Now sometimes people look at "greatest" in terminology in a different manner. They look at how dominant that team was against teams of that era. If you make that argument, Nebraska has a case. It is like in movies. Gone with the Wind is still the top grossing movies if you adjust for inflation but it would not even been in the top 25 revenue generating movie for 2023 if you look at how much it actually grossed.
Adjust Nebraska for inflation and they do have an argument that they are the greatest team. However, they are not beating 2019 LSU or 2020 Alabama (or even keeping it close).