You're framing it as though money is being taken from older FAs and given to young players. That's not what's happening. Money is being taken from older FAs, and some of it is being given to young players, while some of it is being pocketed by owners. Total salaries have dropped two years in a row, and it will continue doing so as the mistakes of the past (Davis, Pujols etc...) expire without similar bad contracts replacing them.
The PA is not going to accept a smaller share of revenues than they had in 2017. There will either be a mechanism for moving that money to younger players, or there will be no baseball. And the PA will be 100% justified.