As far as I can tell, the dark ages were called the dark ages because there wasn't much evidence to be found: writing was less prominent during that time.

> It was a time of transition away from the slave powered empire to decentralized kingdoms and ultimately the Europe of today.

You are seeing the fall of the western part of the Roman Empire a bit too rosy. Compare and contrast https://acoup.blog/2022/01/14/collections-rome-decline-and-f...