They're not doing that. Mac Jones has mid-level NFL starter written all over him and as such he is the perfect QB for New England's system. As @PatsFanNH noted (to the chagrin to so many here), BB doesn't want an Allen or a Mahomes because their drive to make plays can result in mistakes. Mac Jones doesn't do anything splashy, but he also doesn't make a lot of mistakes. And as his ability to read coverages pre-snap evolves, he'll make even fewer mistakes. Brady in many ways, at least in NE, was like that. The only thing that Brady ever did to make your jaw drop was come up huge in clutch moments. But he did that by being consistent and making the right reads, not by making spectacular plays due to immense physical gifts like Allen, Mahomes or Lamar Jackson.