At scale, you would need to factor in the durability of the media. [0] suggests that some types of bluray disks can last 20 to 50 years. Hard drives typically struggle to last 10 years. So if you need to replace hard drives 5x more than bluray disks, maybe it changes the economics.

That's a random study I found on Google, of course, I'm sure Meta has more accurate data on that.

Besides, you need to build the same kind of redundancy in both cases, so that shouldn't influence the choice.

[0] https://www.canada.ca/en/conservation-institute/services/con...