Bioware has always had problems with making believable and nuanced evil/dark storylines, so I wouldn't get my hopes up

People really shouldn't use the "Dark Ages" as an example. It was both very localized; China, India, the Muslim empires and even the Eastern Roman Empire never suffered from it; and not terribly accurate, theoretical knowledge and advancement might have suffered, but if you look a bit deeper there's in fact a vast amount of practical knowledge and advancement. And perhaps more importantly a far wider permeation of them through society (remember that many of the Greek and Roman inventions were quite rare to actually see in effect, while for example wind-and watermills were ubiquitous during the Middle Ages)

Much of Star Wars has also plateaued technologically. Or at least it has relatively plateaued, until a new, but by this time extremely rare, scientific breakthrough allows for more advancement. Also keep in mind that even on Earth weaponry consisted of variations on swords, axes, maces, spears, lances and bows for thousands of years. A bronze sword might have been more bendable and easier to blunt than a steel one, but essentially it's the exact same weapon. Though the out-of-lore reason is simply that people want their Star Wars to be Star Warsy.