Each approach has a different challenge.

For autonomous cars, the challenge is software. It's very difficult to build software that handles all the edge cases mentioned in the article. The hardware (cars) is a solved problem.

For autonomous personal flying machines, you're right that the software is easy, but the challenge is power density. The only VTOL machine that can carry humans a considerable distance without refueling is a helicopter. Helicopters are too large, disruptive, and expensive for everyone to have one. But no one has figured out how to shrink one down and still be able to carry a person.

If you compare the two approaches, one big difference is that software is improving much faster than power density. So my money would be that we solve the first one first.