I really don't care who the 'mentor' QB is, but I think if the Vikings move into the top 10 for McCarthy, he's got to start right away. Taking advantage of the rookie contracts for QBs is the biggest advantage in the game. And Bo Nix is 24 already. If he needs a year to sit (which I don't think he does), I'm not sure he should be considered. A veteran for the back up role would be fine, but not a bridge QB.
Rattler is 23, but he does interest me while still being pretty raw. He'd be the one I'd look at for the sit-a-year approach. And I'd take him over Pennix. He'd be my QB six at this time.