I agree with the origin being the Source ultimately.
I disagree on the higher being entirely dependent on the lower, or on a highly individualistic approach.
An easy way understand the shapes (and otherwise the World of Ideas) being higher than the material world is to consider that the basic shapes are within everything, but the more complex and imperfect shapes are not within the basic shapes.
And otherwise, the material world does not conquer the spiritual, it is the other way around. We cannot destroy the spiritual body of a spirit (intelligence), nor destroy spirit (energy) itself. However, spirit can alter the material world enough that the form is destroyed. This is because the spiritual world is superior to the material. And while things are multiplied here, things are scarcer and more unified in the higher world.
There are many terrestrial scorpions, each in different forms, but they are all unified under the Idea of the Scorpion, which is what makes them a scorpion. And when a talisman is made with Scorpio ascending, and with other factors aiding the purpose, the talisman dominates the earthly Scorpion, and either aids them or destroys them, but the terrestrial scorpion never alters the celestial scorpion.
In Platonism, The One and the Gods are not seen as dependent on the lower worlds. The One did not need for everything to arise out of it, it is perfect as it is, and not dependent on anything else. The same is agreed about the Gods. They are not dependent on the material world, nor do they need to create it.
Here is a longer post touching on that:
Edit: Fixed some grammar mistakes and made some sentences clearer.