The powers of darkness are still part of the spiritual world - they don't become something else when they rebel against God. Disembodied believers are, by definition, also part of the spiritual world. So are God and Christ.

Rebellion against God results in being cast out of his service. God doesn't run the affairs of the spiritual world or our world with rebels on his payroll. They are cast to the Underworld (in the case of the Eden rebel), or a special place in the Underworld (e.g., the offenders of Genesis 6:1-4, who are, to quote Peter and Jude, "kept in chains of gloomy darkness" or "sent to Tartarus"). There are more divine rebels than that in the Bible, but hopefully that scratches the surface enough.

God doesn't save us to perpetuate a particular Christian sub-culture. He saves us to advance a supernatural kingdom that is not of this world.

The truth is that we don't know much about the spiritual world except for what Scripture tells us, so it's unwise to think we can speak with clarity about what a divine being can or cannot do. The tools of analyzing the natural world are of no use for analyzing the supernatural world. For the latter we need rules of logic, and the supernatural beliefs of the biblical writers are quite defensible in that arena.

When biblical material touches on the natural world, we can legitimately use the tools of science. Sometimes that shows us - no shock here - that biblical writers didn't know as much as we now know about the natural world - but God knew that when he picked them, so that alone tells us that "doing science" that would satisfy a 21st century - and beyond - audience wasn't what God was interested in with respect to the enterprise of producing Scripture for posterity.

Why are you uncomfortable with the supernaturalist worldview of the biblical writers? Evangelicals don't want to just say, "Well, the inspired writers were wrong about some of their beliefs about the spiritual world and its inhabitants." That really doesn't work in a confessional situation! So instead we come up with excuses and interpretations that allow us to remake the biblical writers in our own post-Enlightenment image. I understand that impulse, but it's not honest.

We impose our modern worldview on the Bible to make it conform to our intellectual happy place. But we deceive ourselves into thinking this works or is legitimate. We fail to realize that the supernatural things we want to avoid are no more supernatural (or "weird") than the things that define the Christian faith. What's so "normal" about the virgin birth, the Trinity, the deity of Christ, the bodily resurrection of Christ, the hypostatic union of the incarnation (Jesus was 100% God and 100% man)?