How many QBs are satisfied with playing a postion other than QB? If, and I have no way of knowing whether or not this is the case, a QB doesn't think he's getting a fair shot at starting and he's asked to start playing receiver (or whatever) that guy is not happy. This day and age that's a beckoning call from the transfer portal. If McCaffrey wants to be a QB, that's where he should be getting his reps, IMO. Let him have the max opportunity to get better.
I don't doubt Frost would replace Martinez should AM play below his potential. I do believe, though, Frost's judgement is clouded by Martinez's perceived ceiling and he'll be fairly slow to recognize if the time comes to bench AM. The last person to know when someone is cheating is the spouse because love is blind. Loyalty can be blind too. As an aside, has Frost ever said no one loses his job because of injury? That may be clouding the issue too.
I agree McCaffrey's sample size is small. I will say during those few times, and the same with Vedral, the offense looked like it was supposed to. It also hummed at times with Martinez at the helm but with his larger"sample size" it should have been obvious more often that he was "the man," IMO.