I had a BMW from 2007 that had something called "active steering", where an electric motor in between the steering wheel and the rack-and-pinion sort of "adjusted" the steering, which gave it a variable steering ratio (add according to speed) and also stability control interventions (it would countersteer in a slide even if I didn't turn the wheel).
The stability control part is probably the biggest safety benefit of this steer-by-wire system.
Other manufacturers have had similar levels of electronic steering "augmentation" of one kind or another for a long time (e.g. electronically steered rear wheels). In this kind of thing, the safety case is probably that the system only provides small adjustments so that:
1. The driver can overcome any errors in the electronic augmentation system using the main steering system
2. If the system fails, it can switch off and the driver can still steer the old-fashioned way.
In those systems the steer by wire works in cooperation with a mechanical system. Other cars have had backup mechanical steering systems that engage if the steer by wire fails.
What's new about the Cybertruck is it _only_ has a steer by wire system with no mechanical linkages at all. But this is being misreported as the first steer-by-wire system which doesn't cooperate with a mechanical linkage- Nissan has done that for quite a while in some models.
