[@tipssyCalibrator]
Well yes, you'd have to keep that stuff in check, but that's part of a GM's role after all. Creation of nonexistent things doesn't have to mess with your worldbuilding, it doesn't have to be a wholly separate form of magic. It's just a manifestation of a channeler's power, influenced by their personality and creativity. For a simple character example: a bullied emo kid that wanted some kind of badass protector ends up projecting a "demon" summon/stand as his power. It's not an actual demon from hell, but it looks and might even act like what he thinks a demon would because it's that closely linked to the character's story and personality.

As for where it comes from, this is already a setting hinging around magical inner spirit energy projection, with a subset based around creating something from nothing and even manipulating things similar to the things you create on some level. I don't think there's much of a problem if channelers can manifest their energy as a physical being or object.