War and displacement and depopulation caused technological stagnation in some areas for a few centuries. The technology of the high middle ages was actually better in most ways than the Romans.<quoted text>
Actually the dark ages in Britain would've ended around the 11th Century which then led to the middle ages after the Norman Conquest.
The term Dark Ages refers not to pagan influences but the relative lack of progress made after the Romans left in the 5th Century. It took nearly 900years before we resurrected sewerage systems and sanitary toilets with running water flushing systems. In fact Britain experienced a period of regress rather than progress.
You also have to remember that many Scientists of the time had to profess their love of God to avoid being burned at the stake. Those who didn't were perseuted for their beliefs.
Galileo was put under house arrest for believing in Jupiters moons
Charles Darwin had to profess his love of the Church in order to publish the anti-Christian theories of Evolution
Isaac Newton renounced his faith privately but not publicly to avoid persecution.
And while the Pagans may not be known for their scientific feats, we still marvel at Stone Henge and ask ourselves how they did it and why?
Yes, the mixing of church and state was a bad thing and after the separation of church and state again during the enlightenment Christianity retuned to what it was in the beginning. The establishment in some countries felt very threatened by independent artists and scientists and threatened them to proclaim love of god (actually loyalty to the state) but the tyrants always lost because most people were on the side of the artists and scientists.
Just because tyrants have tried to use Christianity for their own power does not mean the religion is bad. Almost all religions have been abused in this way.
If there are no religions to abuse like in Communist Russia tyrants just invent one, like the Stalinist cult of personality. That was something much worse than any medieval tyrant.