I agree. This situation will be tough. The two QB fantasy past 2017 isn't going to happen. A 22 million dollar franchise QB as a backup to Brady just doesn't seem feasible.
If we don't trade Jimmy G, you have to be willing to part with Brady after 2017. There is little chance he retires if he is still playing at an elite level. He may be the greatest NFL competitor ever.
NFL Draft Prospects
The 2017 draft is loaded. Players like McCaffrey, Allen, and Tabor would likely be perennial pro bowlers with us. If Brady can play until 43+ then the trade makes sense.