And this also would explain how they (lower angels) could fall in "time" as opposed to the angels who, being PURE spirit, had to decide to be either for or against God at the first instant of their creation.
Right, it makes sense that lower angels do not have the intellect and purity of knowledge that the higher angels do. This is why lucifer and his followers made their decision, once, and were damned forever. They could rationalize their decision in an instant and either choose God or themselves - forever. It also explains why St Paul tells us that our fight is not against "flesh and blood" but against the "principalities and powers" (both angelic choirs, mid-tier) who rule the world. The angels and archangels would be the ones that "fell" in time. A simple angel, of the lowest tier, is WAY more powerful and intelligent than any man ever born. Just like any man is way more intelligent than any animal.