Yeah, I’m not sure about that. Constantine, Justinian, Charlemagne—all Christians who fought to restore the Roman Empire (really a quite different Empire in the case of the latter) to its former glory.
Churchmen might have been more pacifist than they were during the Crusades, but I think the immorality of the late Empire had much more to do with it.
Immorality, which would have been condemned even in the old pagan Republic, was the source of several of the factors mentioned. The bottom line was the message sent out that state, or the emperor, owes you free food, lodging, and circuses, as long as you remain a mob friendly towards him.
I feel that the brutality of the circuses directly undermined people's interest in serving in the military. They could enjoy real death and dismemberment (as opposed to our reliance on special effects) from a safe distance. Unless you were a condemned prisoner, you were on the arena floor of your own free will to provide a good show for some sort of personal gain.
Join the military, and you spend 25 years of taking orders, and sometimes risking your life. There were benefits of the best medical care available, the best equipment, and a reasonable concern for your food and shelter. At the end of the enlistment, aliens could look forward to full Roman citizenship for themselves and their families.
But in a society that organized itself around mobocracy and free sustenance and entertainment, no sane person would want to sign up to defend the empire.