I agree that Johnson is not a prototypical PF, nor a successful atypical PF. It's the word "official" that's out of place. In football, positions are defined by rule, and jersey numbers are coded to player positions (or at least used to be; I heard something about that changing recently). There is no discussion of positions anywhere in basketball rules. Positions are a made-up thing to make the game easier to talk and think about.
I agree that the Suns have a serious problem at PF. They drafted Johnson to be an 8th man, and that's what he is. I think I remember the team saying that they saw him as a future PF when they drafted him, but I could be wrong about that. In any case, if they drafted him to be a true starting PF, they made a bad miscalculation, although not so bad as the one they made with Smith.
Crowder should be a 20-mpg energy/grit guy off the bench. He's forced into the starting PF role by default. If Ain'tn were a realistic option for low-post offense, the Suns could get away with PF by committee. But instead they have no one who can create his own shot in the paint, and that's a pretty serious weakness.