The interesting thing about an empire is how difficult it is to cover every square inch of it in all times in practice, and not just on a map. The sunway is pretty far from Mor Dhona (where the Crystal Tower is) and it and Dalamud seem to have been the biggest projects undertaken by the empire. It's possible the areas the sunway went through were poor areas of the empire that weren't especially a concern to Xande and company. It's also possible that the greatest innovations of Allag occurred relatively late in the empire's life which could be a significant part of why the Crystal Tower and Dalamud are the only consolidated sources of what we think of as Allagan technology. It's also possible that they had some nudging from our friends, the Paragons, given what we saw with Gaius and Ultima Weapon in the main scenario.

I doubt we'll ever get an answer, but those are my two biggest questions about the Allagans: how widespread WAS the Allagan high technology that we all think of with glowing lines and interlocking parts during their heyday, and for how long was that technology key to their reign. Obviously it had been around for a while since I doubt Dalamud or Ragnarok were weekend projects, but it'd be interesting to see how long they had been a part of the society of that era as a whole.