The benefits of the switch to a 3-4 is being able to bring pressure from multiple directions. Also very cost effective from a salary cap perspective.
Being able to platoon and rotate pressure while also keep offenses guessing is going to really pay off for the invested resources in the secondary.
3-4 is actually more expensive.
You have to pay a premium for both OLBs, and DEs.
Where as in a 4-3. SLB usually makes peanuts, and doesn't play more than half of the snaps.
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Onto '22.
It will be better than last year, because anything is better than another year of Norton. (Who was oddly praised by people who don't know football last year, and then they were totally cool with him being fired. Absolutely hilarious.)
Rookie DC, installing a new defense, a lot of new pieces. It's hard to make any bold claims at this juncture, but it will be better than last year.