I agree with Fields needing a different perspective, possibly via a veteran QB. However, that could/should also come from the QB coach.
I disagree about it being tougher on defenses if the backup QB isn't a carbon copy of Fields. Who do you think defenses would rather prepare for, a QB like Peterman/Semien who they know are no threat to run and will be in the pocket, or a mobile QB like DTR/Malik Cunningham who are threats in the run game via the read option, bootlegs and scrambles on broken plays?