Whether it was Garrett or not, one thing you said ""just beat the man in front of you" from the 90's" isn't just a 90's thing, has been true ever since they started playing the game and it's still true today. EVERY play is designed so that EVERY player beats the man in front of him for it to work. Just about every play on any team where that play didn't work with the exception of the QB throwing an incomplete pass failed because someone didn't beat the man in front of him. If a RB gets tackled for a loss or only for a 1 yard gain, it's because a linemen didn't beat the man in front of him. Beating the man in front of you will exist as long as they play football.
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I think you are misunderstanding to what level Garrett took it to.
I understand that execution is a part of any team sport, but in Garrett's era, it did not matter if there was a mismatch that gave the opposing team a big advantage, he REFUSED to change his scheme or game plan to counter act it.
The absolute easiest example of this is 2017 game of Dallas vs Atlanta. Despite Chad Green being absolutely over-matched by Adrian Clayborne, Garrett never adjusted and left Green out there all alone to get his butt kicked. And it was not like Adrian Clayborne was a great passrusher either as in that SINGLE GAME, Adrian recorded more sacks (6.0) than he had in 5 of his 7 "full seasons" (2 seasons he played 3 or less games). He only beat that SINGLE GAME sack total by his Rookie Year (7.5) and his 2017 year (9.5). (How mediocre are you to get 6 sacks in a game and still fail to hit double digits for the season?)
Another example of the refusing to help players via schemes like the use of "Rub Routes" in the NFL. It's not a every play tactic for most teams, but where you would see it about a handful of times a game for most teams, we may have seen it a handful of times in a decade.
I am not suggesting that players are completely free of blame by not being able to beat the man in front of them. What I am saying is that Garrett was incapable or too stubborn to adjust when a player was over-matched, or regularly implementing a scheme or tactic to put players in better positions to succeed.