You might have chosen the worst example for your point, it is super duper easy to register a car online. I registered both of my cars online, the papers arrived in a week but I was able to drive and insure the vehicle without any interruptions. They give you a printout to carry around while the original registration papers arrive, but the police already knows whether the car is registered or not and will not bother you.
> it is super duper easy to register a car online.
If you are in possession of the title of the car, yes.
However if you lease a car, the leasing company will just post the lease to the Zulassungsstelle so that you will not be in possession of the title at any time. So it will require you to go there in person.