Then you're misunderstanding the requirements to be a type 2 concept. In order to be a type 2 concept, the thing in question simply has to form reality, have everything in reality participate in it, interact with said things, and changing said thing would change whatever participates in it. And it has to transcended of reality
Grandfather Spider's Shadow Magic, the very thing he embodies formed the reality of the Spiral, and everything in it, and binds the aspects of existence together. If they're embodiments of existence then their fundamental nature is conceptual, because they embody the very thing they are stated to embody. Otherwise they wouldn't be considered the very embodiments of whatever structure is mentioned.
I don't know what you mean by the second point. The scans literally state they embodied a new school of magic, an aspect of existence
The schools of magic are what formed the Spiral, especially Shadow Magic. I don't know if you know the lore of wiz, but existence was created through Spider's Darkness and Shadow, and Raven's light and order, the dualities beyond the great wheel of existence, which is beyond the Spiral. Which leads to your third point; It was already accepted by numerous mods, notably Ultima. It is not vague and saying it is flowery language isn't a rebuttal. It is your job to prove and say why it is iffy. You aren't even arguing anything. Therefore, it transcends reality as accepted numerous times.
Proof he gave them significant power? Sure. Here you go. These guys started at town level and jumped to Low 1-C, and stated in their battles that they were using Shadow Magic itself, thanks to Grandfather Spider. In lore, when Morganthe met the Shadow Magi, she released Shadow Magic for anyone to learn, you just needed to be decent in magic. It is there to access because it literally forms reality and binds the other embodiments of existence together, which funnily enough, are Spider's children.
Fodder users of shadow magic stated they can alter reality iself, so yes,Shadow magic definitely gives a significant amount of power.