I mean, this contest doesn't really matter. Whoever loses here will still win the 3-way pretty handily, imo.
Byzantines were the reason the *Arabs*, not the Turks, didn't conquer Europe. They stopped the Sassanid Persians from taking the city in several sieges, their Avar allies in 626, and later the Arabs and so on.
This is pretty much fact. Every enemy of the Byzantines ran rampant throughout Anatolia, sacking cities, destroying armies, etc. Only to be stopped at the walls of Constantinople. The walls, moreso than the armies, are the reason the empire survived, and Constantinople wasn't sacked like Rome.
When were the walls built? Mostly in Roman times. First under Constantine, then Septimus Severus. The last great expansion of the walls (minor improvements were made to the fortifications throughout history) were the Theodosian Walls, which were started in 408, just 13 years after the date given for the "founding" of this Empire. So I very much would like to attribute the survival of the Byzantines to the Romans as well, since everyone who built those walls was born a Roman citizen.