I wouldn't even consider our defense a 3-4 or 3 down lineman look. We ran so much nickel and sub packages, often with 4 lineman that I would consider nickel with 4 d-lineman/linebackers on the line in some variation to be our base, which is consistent across the league now.
Frankly all the talk about alignment and how many down lineman you have is pretty much irrelevant anyways. That matters a lot more in the run game, not so much in the pass game. The more crucial aspects of a pass rush is what you do when the ball is snapped.
To have a defense as bad as our 2020 product, you have to have both personnel and coaching problems. We didn't have the players to win 1v1 matchups in the pass rush, but then we also failed to bring additional blitzers to help since we weren't winning with our 4 man rush.
JRob knew our personnel was a weak spot and threw the kitchen sink at trying to get someone to be a productive pass rusher. It failed, but at least he tried. Hopefully there is some better talent in this years draft and they target that as a position of need.
I don't know how blind the coaching staff had to be for it to take them 15 weeks to figure out that blitzing would be the only solution to helping a bad pass rush, but that was an egregious mistake that I can only hope is fixed by an incoming coach.