Are you sure they survive for the time period you intend them to? When I was a teenager, I though the DVDs and BluRays I burned would be forever - 15 years later I am very unhappy to find that some of them started to crack and flay - it's a pain to keep checking them. Nothing like the guarantees a NAS + Cloud backup could provide.
NAS also fail, and cloud backups can be taken away without notice.
Hence why multiple copies.
sure, but NAS and cloud doesn't fail at the same time. Also NAS provide some redundancy in-house as well. Whereas BluRay is a single copy - even if you burn multiple copies, they degrade at the same rate.
That would be true if I would have done all copies on the same day, and never duplicated disks.
You basically imply that you have a NAS that you regularly take backups to BluRay?