Since the realistic competitor here is probably magnetic tape, current-generation (LTO9) media can transfer at around 400MB/s, taking 12 hours and change to fill an 18TB tape.

Earlier archival optical disk formats (https://news.panasonic.com/global/stories/798) claimed 360MB/s, but I believe that is six, double-sided discs writing both sides simultaneously, so 30MB/s per stream. Filling the same six (300GB) discs would take about an hour and a half.

Building the library to handle and read/write in bulk is always the issue though. The above optical system fit 1.9PB in the space of a server rack (and I didn't see any options to expand further when that was current technology), and by the looks is 7 units that each can be writing a set of discs (call that 2.5GB/s total).

In the same single rack you'd fit 560 LTO tapes (10.1PB for LTO9) and 21 drives (8.4GB/s).

So they have a bit of catching up to do, especially with LTO10 (due in the next year or so) doubling the capacity and further increasing the throughput.

There's also the small matter that every one of these massive increases in optical disc capacity in recent years has turned out to be vapourware. I mean I don't doubt that they will achieve it someday, but they always seem to go nowhere.