The so-called "Dark Ages" were not solely engendered by Christianity, and even the arguably negative characteristics of Christianity in late antiquity were ultimately shaped by prevalent outside factors and not inherent to the religion itself. It literally took many centuries for Roman civilization to collapse, and the root cause was that (like many ancient societies) it was basically predicated on plunder and conquest, so the whole arrangement began to collapse like a slow-motion trainwreck when they could not effectively plunder anymore.

There might have been some hope that it could gradually transition to a somewhat more modern style of economic development, but this was hindered by the Barbarian invasions especially of the Huns, so this whole dynamic only really took hold much later, in the Middle Ages.