Well, in this case, we don’t need to argue about theory. The Joby has a tested range of 150 miles. They also tested it with hydrogen fuel cells and got >500.

Right, so when you factor in the legally required reserve flight time the battery powered Joby is only capable of very short hops. And that's fine, it's still potentially useful on a few routes and newer models will improve over time.

Sounds about right. A plane of comparable max take-off weight, a Piper Malibu, has a range of ~1500 miles (with reserve remaining).