I'm going to go way out on a limb and suggest that Parsons, Diggs, and Lawrence are the keys to the Cowboys defense. If you are looking for additional firepower on defense I would say that Osa, Cox, and Joseph are more of a key.
I expect those three 2nd year players to improve significantly from their rookie seasons and when you really think about it, wouldn't last seasons defensive draft yield far more potential?
Fowler was a bust whose fortunes magically improved when he signed with the Rams and played next to Aaron Donald for a season. That was his only double digit sack season. His other five seasons average out to less than 5 sacks a season. Take that one season out and he's practically had a career as a a non-factor.
LVE could revive his career if he can stay healthy.....a very big "if". I am very hopeful he can persevere and contribute to the team but I wouldn't call him a key.
I don't know why Hooker would be a key. Ironically, the Cowboys were considered extremely weak at the safety position prior to the 2021 season. Halfway through that season Wilson was almost an afterthought. Kearse played great. the team has some young prospects from last season and this one as well . It would be great for Hooker to breakout in 2022 but it's not a necessity when the team still has Kearse and Wilson..
Actually, all things considered, if you wanted to point at a specific position and claim it is a key to the Cowboys success on defense, it would absolutely have to be at defensive tackle.
Considering the way in which teams successfully attacked the Cowboys last season, the first order of business has to be stopping the run down the middle. No matter how hard LVE plays, he's not going to do much if the DT's can't slow the RB's down.
It would be entirely reasonable to claim that Osa, Gallimore, Bohanna, Ridgeway, Trystan Hill, and Carlos Watkins, as a DT unit will be the key this coming season.