Pyramids have no traditional esoteric significiance. The whole pyramid power junk is just that; junk. It's massively New Age and was made up by some New Age occultist who spent a night sleeping in the pyramid.
The shape was more to show the movement of the rays of the sunlight, and to catch and shower them downwards, and was a more perfect shape than the mastabas and the failed pyramids that came before. It represents the primordial mound, but it's shape isn't the shape of the primordial mound (otherwise it wouldn't be a mound ;)).
It's interesting you brought up Aset (Isis) as she's actually quite a lovely netjeru in many of her forms, and quite a terrifying one in many of her others.