It's not a highly redundant enterprise solution, but it's decent for home and small business users, especially since the alternative is usually 'nothing'.
Only Qnap offers ZFS and Synology offer BTRFS. And none of these file system are default option. ( I dont think they do scheduled scrubbing by default either ) They are also only available on mid range model. Qnap had third or forth security issues with Bitcoin ransomeware. Synology requires lot of work to turn off All internet facing features. To the point they dont want you to do it because all Internet facing features are their product differentiation. I think most user want more like a DAS ( Direct Attached Storage ), or NAS that is only accessible via Intranet.
Once you have that setup, a DS220+ with two 4TB NAS Drive and a usable 4TB storage cost $500. ( Or $400 if you use non NAS / Long Warranty Drive )
I am not sure if $500 / $400 for 4TB is cheap or affordable to average consumers.
Unfortunately there aren't much R&D into optical disc technology. Would have been nice if we get 1TB per disc.
That said as said in the other comment M-DISC is really the way to go. Burn a couple of these, store them separately. They're rated for 1,000 years of storage if stored even somewhat properly. You can get them in 100GB sizes, so perfect for this kind of job. Burners aren't crazy expensive, 100GB discs were around $10/disc last time I bought.
[1] https://kobol.io
A stack of DVD's in a book shelf.