I'd like to make clear again that whether or not Intercession Magic is accepted or denied isn't up to me nor is it my primary concern. This piece is separate from it and I specifically tried to gear it away from the pseudo-biblical influences of the previous magic, and of the Human Faith. In part, the Humans have always had the blessing to go to the Seven Skies, I'm not excluding all others, the approved or previously set blessing that was given to Humanity is supposed to set them apart.
As for how the Seven Skies is stronger, that is how I interpreted it from Benbo's lore on the Immortal Planes, as it is said to connect all the planes together. It wouldn't be far of a stretch to imagine that a plane which is connect to all others was the place from which those other planes were erected, and thus, where the creators of those separate planes originated from. How it's described, well, the Creator is believed to have created it, the majority of humanity believes it to be so. Would the font's strength even be a major factor if it's power is constantly being split among the souls of Human descendants, thus drastically decreasing it's potency? I determine how powerful it is by how it could effect the mortal plane, that being explained in the INFLUENCE section as being similar to that of the spirit realm, mostly because that can already be gauged to some extent
In reference to the Spirit Realm, yes they share similarities in that they both house spirits, and that they are both Immortal Planes, but the Spirits who inhabit them, the way in which they might influence Axios, and the divisions of the Planes, I think, are different. Honestly if we're speaking up on the similarity of various Immortal Planes, why is it a major issue here when there are three that would fulfill or work the same already? That being in reference to Xan and Tahariae, purity and order, they both fight evil on the server, they both share basic traits, and yet they're separate from each other.