If you mega-pay a player (Allen in this hypothetical), and also overpay 2or 3 players you end up in salary cap jail. Jailed teams are less competitive.
Rookie contracts are very salary cap friendly. That's why the draft is so critical to success. A good draft gives you financial flexibility to pick up assets in free agency.
To the OP: my opinion is that in 2022 if Josh Allen is lighting up the league, back up the Brinks truck to his house.