Our OTAU architecture uses A/B system updates [1]. Core idea is that both the kernel and the rootfs (read-only) partitions had 2 different bootslots in storage, and the OTAU would only write to the bootslot that is unused. Hence, if something went wrong, the system would automatically fallback to the previous version by just switching the bootslot used. Over the numerous years that that architecture was used, I couldn't find a single post-mortem that resulted in devices being bricked. Something to note is that the rootfs partition was overlaid with a writable partition for persisting state data etc.
Now that was a $two-figure USD device, not a $5/6-figure USD electric SUV. Is this a cost-cutting measure? At those price levels, doubling your NAND size is not even half of a percent of the total cost of the vehicle.
Unless there was a serious issue that the used bootslot corrupted the unused bootslot, then I don't see how this could have happened.
It's saddening that car manufacturers are so unserious about the code they're deploying.