This part of that support article is pretty damning:

WARNING: Back up your data before you restore the firmware on your Mac. When you restore the firmware on a Mac that contains an Apple T2 Security Chip, you are restoring the firmware on the T2 chip and on any volumes on your internal SSD storage. When this process is complete, any data on any SSD volumes is unrecoverable.

So this means that a firmware issue can lead to total data loss? Of course you should always have a backup, but nevertheless...