Surely you're not suggesting that the objective truth of an idea may be ascertained by its popularity?
I do not dispute that the remnants of the Roman Empire were sucessful in spreading Christianity, just as the British Empire spead the English language across the globe. None of that addresses the objective truth of Christ's resurrection or serves as proof thereof.
Popularity? Christ was so popular, the Romans crucified him. Even those who hated him and had every motivation to discount or hide the fact of His resurrection did and still use his birth as the reference point for all of human history.
Popularity? There is no historical figure as popular as Jesus Christ; not even close to his. What other reasonable explanation could there be that sets him apart from every other person born in the history of the world. Could it be that he wwas the only one resurrected from the dead?
Christianity was not popular with Rome. They killed virtually all of Christ's disciples and uncounted thousands or millions of Christians until much later.