Fiberoptic cables are limited by the diameter of the cable. A mirrored duct can be as big as you need it to be. We’re talking about enough light to brighten an entire room. A half-inch fiberoptic cable isn’t going to do it.

Solar tubes are very effective at bypassing attics. That’s probably their main application, but if we’re talking about constructing post-apocalyptic catacomb cities, where we already need some sort of central ventilation shaft and duct work, then it’s not like we need to retrofit it to some structure that isn’t designed for it…