It is not true that Christianity was popular with the "urban elite." Christianity was a primarily urban movement, hence the "pagan" slur, but the actual urban elite, the senators, aristocrats and magistrates, were highly anti-Christian. It was the urban non-elite who were most attracted to Christianity. These urban non-elite were not "hellenised", in the sense of being conversant in Greek philosophy. They spoke Greek as the lingua franca but that is not the same thing.
What I think you are confusing is that pagan philosophy, e.g. Platonism, had led many of the educated pagans to be sympathetic to monotheism, and so in a way Hellenistic philosophy primed the Roman world to be more receptive to Christianity when it arrived. But those actually educated in this pagan philosophy, i.e. the elite, were the most fiercely anti-Christian group. It is paradoxical, yet it is true.
