A 7.8 would destroy much of the infrastructure in S. CA. then the fires would take out much of the rest. Serious damaging aftershocks would go on for many months possibly triggering other faults..
I remain skeptical.
I lived in Southern California years ago and the area is huge and really spread out—larger than my current state (CT).
It would be like claiming something would “destroy” CT—makes no sense.
The Northridge quake was a good example—totally devastated Northridge but had minimal impact for most of the metro area—just scary shaking.