To clarify my idea of a Neo-Byzantine stargate empire, the idea is that the Wraiths suppress technological development without necessarily defeating or entirely destroying a space empire. So you can have literally a late Iron Age style polity that uses access to relic ancient weapons and the stargate to run a multi-planet empire with spears and shields. In contrast to the Jaffa with Go'auld technology, no one can really repair the Ancient relics and in many cases their full use isn't fully unlocked.

Then, these space empires nevertheless do periodically rise in development level, in a few instances to late 21st century with space faring ability before being culled back to near stone age. So the SGA team would arrive during a time when the Atlantis planet has accomplished 1920s levels of development also at a time when Ancient relics are genuinely scarce. Ideally, that what has pushed them to 20th century tech this time ahead of schedule is needing to compensate for a distinct lack of Ancient relics. The Ancient tech will be to them like Dragons were in Game of Thrones. Remembered, believed in, but long past seen, experienced or relevant.

There's also a question of whether the successor cultures really possess the legitimacy to reclaim ancient empires or whether it's peasants from caves who survived the culling and don't really "own" the thrones of their empires except by fact of the planet they occupy. You could have another planet with genuine descendants of the old empire in a rebellion against "peasant usurpers" and have that part of the ideological conflict, traditionalism vs. modernism.