NIL and the Transfer Portal got him, plain and simple.
Whenever there was a level playing field, he's always almost been just a solid coach - above average in some areas, below average in others, but all-in-all just solid.
Prior to his time at Alabama, he had one season in five at Michigan State where he didn't lose at least 5 games and he never went undefeated, he had one season in five at LSU where he didn't lose at least 3 games and he never went undefeated. We saw what happened in the NFL when he couldn't constantly have things his way and every team had relatively similar talent and resources. It wasn't until he arrived at Bama, got the in-state SEC offices squarely behind him in all areas from scheduling to officiating to enforcement (the examples of each being too numerous to mention here), that's when he finally got on a roll, so to speak.
His true 'acumen', if you want to call it that, his legacy, has been his ability to recognize loopholes in the system and masterfully exploit them to his advantage... the rampant corruption at all levels that we saw early on didn't continue nearly as badly as time went on, but then, it didn't need to - once you build momentum and success, it becomes much easier to sustain.
But that's over now. The current environment simply doesn't lend itself to that any more. If Nick can't step on the field with a three-to-one talent advantage, if he can't show up at work knowing that he's going to benefit from preferential scheduling and treatment from the powers that be, a lot of his power and mystique fades pretty quickly.
I don't think anyone can argue that he hasn't been the most successful college coach in history, that's obvious... but while I'll forever be grateful to him cutting through the BS here at LSU as a stepping stone towards his own success, I'll never think of him as 'the greatest' by any measure. At the end of the day, for most, results are all that matters, and that's fine... but for someone to be 'the greatest' in my book, how they did it matters as much as what they did.