Yes, the ferry pilots were an exceptional group! The skill to go from one plane to the next is gained through doing it, in a well trained and supervised environment.
It's great that Raab has time in the PA-28 and Citabria, a good combination for skills development! Raab, you'll find that the larger aircraft are easier in some respects, like not so gust reactive as the Citabria, but on the other hand, that added inertia makes it more difficult to correct things when they start to go wrong.
But importantly, as you mentioned, you'll want some more experience in general, and on the larger type, before you start carrying lots of people. Letting alone the simple responsibility for the people, they can be a distraction to you while you're flying, or even a problem when they yell "Hey whats' that!" as you're just lifting off.
In Canada, we're a little less government regulated when it comes to being type trained, a pilot can pretty well go from one type to the next within a class, and self train if they like, but the insurance company will still take quite an interest. It is likely them who require training, and supervised time on type, based upon the pilot's experience, and that's a good thing.