Angels can fail because God allows them to make decisions and they are lesser beings than the perfect God. They can go astray, but the task is legitimate. God never tells they aren't allowed to instruct people - "just shut up and babysit them".

God wants the world to function in an orderly way, not a chaotic way, so teaching humans to do what's right and what will make for the happiest life isn't going to be off limits.

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 like to pretend the core ideas of the faith are more palatable or workable within our modern rationalistic approach to Scripture than the stuff we want to call "too weird" because of our own intellectual sensibilities. The truth is they are not. So we come up with interpretations to eliminate the weirdness of the biblical worldview that makes us uncomfortable. Problem solved!

If you don't have the worldview of the people who produced the Bible - under inspiration no less, - you can't understand what they were trying to communicate in many respects. Biblical people weren't modern people. That's self-evident no matter how much we try to deny it.

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.

If I were one of the gods who just wound up supervising humans, I'd want to influence the decision-makers to live according to the morals that Israel would eventually get in the Torah, and to teach those same principles to their people. I'd also want to make sure they worship no other god but the Most High.