I think hard-drives would be more efficient and less costly although, as you mentioned, running them constantly would be an expensive consumption of electricity. But so would running all those optical disks, too. But no one would do that. They’d file those away. Just like I could ‘file away’ my hard-disks.
Long-term hard disk storage presents two issues to me: (1) I want to have a backup drive, too, perhaps using an identical drive-model, and I’d store them a distance from one another (to prevent a single fire, a single theft, a single natural disaster from claiming both.
And (2) hard drives can store tens of thousands of files. How do I keep an accurate and correct catalog?
Then, there’s hardware obsolescence. Every ten years or so, I’d probably need to migrate the data from one kind of hard-drive to the next generation. Ten years ago, the SATA hard-drives were becoming common, but the IDEs (from 1993 onward) were common enough.
Today, there are few modern motherboards sold with IDE connectors (ASRock has some, but I suspect this will be the last year those will be available).
We might have motherboards, in 2023, that accept SATA connectors, but perhaps not.
So, would I need to store a running computer to host those various hard drives? Sure, why not? If a newer archival drive failed, then perhaps I could power-up an original computer and connect it to those drives.
I think HDD connectors and limitations aren’t any more prone to change (obsolescence) than Optical Drives because they share the same connectors and electrical requirements.
But I’d always want “one more backup copy” somewhere.