Part of the reason I settled on optic disc was to remove the need for multiple backups.
Yes, understand. There are additional risks writing to an optical disk. For example, what if the drive for some reason was out of alignment or marginal in some way? I have had disks which I have written (just DVD, not BD) which when I tried to read a decade later were not readable. I had to toss them. Since you are knowledgeable it might not have been an alignment issue, but you get the idea.
When you need to restore from backup in X number of years is there even going to be a BD drive available to read them? I have read numerous articles about attempts to recover contents from old computer tapes. In most cases they had to scrounge around museums to find equipment that could read them. I don't see many VHS tape recorders available for purchase right now. BD players are being discontinued, e.g. Oppo, Samsung. Although not the same thing, that means that whole market is shrinking.
Let's say that you still have your BD drive around and it still works when you need to do a restore. Will the equipment that you want to use to read the drive even be able to see it? Will it have the drivers?
A lot of these issues also apply to magnetic media. Magnetic media in addition needs to be refreshed. But something like 344 million drives have been shipped in the last 12 months which means that there are billions of them out there. Cloud backup services keep expanding. Backblaze has over 100,000 backup drives. And that is just one company. Consequently there will be support for magnetic media for a long time. There will be data recovery services available to recover data from the platters even if the physical drive itself fails.
So my posts about having multiple backups isn't motivated by theory, it is by actual, painful experience. I have seen way too many posts in MacRumors from people who have lost everything because they didn't have any backup.