In the years that I've been riding, I've seen that horsepower tends to be the least of the worries for new riders. They're far more likely to suffer from "failure to turn" than they are to run into the back of a semi, at 200 Kmh. Skills are more important. Don't nanny; mentor.
A 750cc cruiser is a fine starting bike. Why limit people, by not permitting that choice?
I guess I and most of a continent packed full of more riders would beg to differ. Mentoring takes mentors....there's some but not enough for all riders so then with your anti-nanny stance riders would be waiting for the bottleneck to clear before they can ride. In effect you'd be denying them the opportunity to ride by proxy by creating this bottleneck? I don't see graduated licensing as nannying...I see it as a sensible attitude brought about many decades of advice from more experienced riders and the best argument for it is that it appears to work well where it is instituted.