They're defective by design when advertised as NAS drives. It was impossible for them to work as users expected given their construction. It wasn't defective in the sense that there was a manufacturing flaw that made some of them fail, but in the sense that it was inherently unfit for purpose. If you design a car's brakes to fall off when they get hot so as to protect the braking system at the expense of the car, even if it works as designed, it's still defective.

I don't know how to reply to the rest. If you think it's a good idea for Synology to make their systems not work with even known-good drives from reputable manufacturers, I don't think there's likely to be a common ground we can find to discuss it further.