Gibbon got into trouble because he attributed a lot blame for the fall of the Roman Empire to Christianity.
He frequently unfavorably contrasts the otherworldly focus of the later Roman citizens, with the energetic practical outlook of their ancestors, and with the warlike nature of the barbarians.
He also has a lot in there on the various doctrinal disputes and heresies, and subtly makes fun of them and the disputants.
You got it right IMO that God’s plan did work out as Christianity provided the foundation for the tremendous moral and scientific progress which the western world has had.
A BIG yes to you.
It also elevated women (via Mary) to the status of human beings, instead of chattel.