Might be true, but I don't see any aspect of that which is relevant to this event:

* Data single obviously means losing a single drive will cause data loss, but no drive was actually lost, right?

* Metadata DUP (not sure if it's across 2 disks or all 3) should be expected to be robust, I'd expect?

* I certainly eye DM-SMR disks with suspicion in general, but it doesn't sound like they were responsible for the damage: "Both DUP copies of several metadata blocks were written with inconsistent parent and child generations."