Sure, this kind of technology works fine. Except that it might be difficult to find people who how maintain or repair the fancy (pressurized? oil-filled?) copper cables or the modems, and finding parts might be interesting.

I did some enterprise network work ~20 years ago, including fiddling with some inter-building links, rummaging through closets, and visiting the inside of a legacy campus-scale analog phone exchange, and I’ve never even seen the kind of equipment that can send data at an appreciable speed (even by 1990s standards, and even with repeaters) over copper at a range like 100km.

In contrast, single-mode fiber has improved over time, but it’s not obsolete, and it has maintained a remarkable degree of compatibility over the years. New transceivers largely work on old fiber, old transceivers work on new fiber, etc.