If he were a workout warrior, who had a great Combine but hadn't done much on the field in college, I would agree. But he had a top 1% combine PLUS consistent college production in a top 5 conference. Short of injury he is a Can't Miss prospect.
In terms of generational, what people are saying is this: if he stays healthy, he will be a Hall of Fame back. Lots of HOF careers cut short by injuries, so you never know, but he has that type of ability. How many guys playing now have that kind of ability? Gurley, Elliot, Fournette. If you want to be cautious and wait to see some NFL action, then you could reasonably rank all these guys above him. However, I think you could make the case that his skills are more balanced than any of these guys.