> with no technology to speak of for the 1000 years after Roman Empire
While it's true that some technology declined in the West, it wasn't as dramatic as you've suggested. Popular media also often exaggerates it.
https://www.britannica.com/technology/history-of-technology/...
Adding USSR into the discussion greatly increases complexity of the discussion. From analysis I've read, central planning is supposedly fine when country doesn't have much industry, because to start things up, it can provide essential investments and starts organizing production. But when country is somewhat developed, efficiency starts to matter and top-down approach to decision making of central planning vs bottom-up decision making mechanisms of markets produce different results. Politics and other things are important factors too, but I think that would be too much for this discussion.
No, they were more advanced in certain ways, but the original contention is correct that they were less advanced in others. Notably they were unable to build domes. They were also less productive, so less advanced in an overall sense.
https://en.wikipedia.org/wiki/History_of_medieval_Arabic_and...
The fall of the Roman Empire is a pop history trope at this point.
More than that, technology continued to evolve. The Romans had nothing like Medieval plate armor, for example. There are many examples of better tech from the supposed "Dark Ages".