The Dark Ages began with the fall of Rome in 476 a.d. and ended with the Christianizing of Europe and crusades.
The spread of Islam produced exactly the opposite effect and is probably evident nowhere more than Persia.
Confucianism, as you say, was a reasonably good way of running things, but was undermined by the Mandarin bureaucrats who did much the same thing to the clever inventive Chinese civilization starting in about the 13th century which our atheistic liberals are doing to western civilization today.
Without the moral underpinnings provided by Christianity, a meritocracy, however well-intentioned, is eventually distorted by those who gain control of an amoral legal system to set the rules.
“Without the moral underpinnings provided by Christianity, a meritocracy, however well-intentioned, is eventually distorted by those who gain control of an amoral legal system to set the rules. “
Without the moral underpinnings provided by Christianity, any political system becomes corrupt.