I don't disagree, I just don't think there would have been as strong of a central church authority because it wasn't grandfathered in as a former Roman institution with all the power and influence that came along with that.

Once the Roman emperors decided Rome was Christian, a lot of Europe was suddenly Christian. Iberia, everything west of the Rhine, the Balkans, Anatolia, and the western part of the Middle East. If Rome hadn't forced that, Christianity wouldn't have spread as quickly and might even today still be one of many different sects.

Islam might have spread through Europe instead of being stopped in Iberia and the Balkans. It's impossible to know what Europe would have done with Islam, but early Islam was a lot more tolerant of other religions and valued education, knowledge, and progress. We might not have settled in to some centuries of most people thinking humans had discovered everything there was to discover or physics being held back by people offended at the idea that the Earth isn't the centre of existence. Colonialism might have even been different because Islam didn't stamp out existing cultures like Christianity did (though again, who knows what it would have evolved into by the time people were figuring out how to navigate the oceans, because Rome also used to be like that).