To be honest, I don’t understand your problem. During the period experienced and anticipated by the New Testament, both for Israel and for the early church Caesar was king (‘We have no king but Caesar’: John 19:15) and Rome was the oppressor of the people of God. Jesus won a victory over this supreme enemy of the people of God (your reference to Col. 2:15 is apposite), but this victory became a concrete historical reality over the coming decades and centuries as communities of his followers pursued the same narrow path of faithful suffering. In the end those communities emerged from under the hegemony of the ruling paganism as the ideology of Roman imperialism, with the divinized emperor at its pinnacle, collapsed. The oppressor of the people was overcome. How is this not historical?

But I would also stress that biblical interpretation is not bound to take account of what actually happened. Paul did not know exactly how things would work out. That’s why he creates his narrative of hope out of Old Testament material. What he needed to do was communicate his prophetic assurance that the principalities and powers would not overcome the church, that God would eventually ‘judge’ the enemy of his people, and so on. The point was that in the not too distant future (you can’t keep ignoring the pervasive stress on imminence) the church would be delivered from Rome in much the same way that Israel was delivered from the Babylonians or from Antiochus Epiphanes.

Judgment on Babylon did not happen exactly or literally as it is described in Isaiah, but in the end this enemy of Israel was defeated by the Medes (cf. Is. 13:17) - God’s judgment was executed as Isaiah had prophesied. The same language is used in Revelation (cf. Is. 21:9; Rev. 18:2) to describe the destruction of the oppressor of the church. As in Isaiah, the political event or transformation is interpreted through the symbolic language of prophecy as an act of divine judgment. The prophetic or apocalyptic language places the people of God at the centre of directly relevant historical developments.