Don't recall where I read the insight, but it said the secret of Brady isn't extraordinary athleticism (clearly) or off-platform improv (clearly) but in executing the on-script stuff perfectly, every single time.
Some guys can run the plays correctly but without the physical gifts to execute with live bullets (see: Peterman), and some guys can get by on athleticism alone (see: Lamar). If JA17 ever gets close to the Brady standard while being an absolute lab-hatched QB unit and having broken play superiority as a safety net, has the sport ever seen anything like that?