You won't ever see a 1st round pick or a starting QB willing to Do The Taysom. Pride and making business decisions protecting their wealth, health and longevity all trump becoming a 2nd string QB with limited snaps at the helm while risking their necks on every other snap they get. It takes an unselfish player that just wants to play no matter what he is asked to do. That's who Taysom Hill is as a person, a teammate, and a player. Not knocking the other. Just saying.
Fields isn't that guy. Granted, Fields has the size and speed and can throw but you'll never see him on any type of special teams play or blocking as a TE. Also, though Fields is slightly bigger (6' 3" 228 lbs.) than Hill (6' 2" 221 lbs.) I doubt you will ever see Fields make a steady habit running the QB power. Fields is more of a break containment from the pocket and take off type runner whereas Hill lines up and you know what's coming and still can't stop it. One is like a Deer. The other is like a Bull.