Well, for my money, I've never made the argument that NOT eating primal is a one way ticket to the grave. Between your father and the plenty of cultures that eat grains, I wouldn't be able to.
But I think what we're looking for in the PB is 'the ideal.' What were we meant to eat? What were we designed to eat? How are we supposed to live? So on a sliding scale we'd have the PB on the one end and the Standard American Diet on the other. I guess your dad is somewhere in the middle. I don't know that that's a 'bad' place to be, but in my own experience moving closer to that PB ideal has been hugely beneficial.