I know nothing about the story/game you're talking about, but I think this is an important and common misconception, and fanfiction that addressed it directly might be worthwhile.

It shows up in a bunch of places in fiction. Grant Morrison's Invisibles and the Nobilis and Unknown Armies RPGs, I think. A particular bit is that something very much like the present-day real world shows up as a part of the greater reality, setting up the plausible deniability that the world might really be like the postmodern meta-reality described.

I'd love to see stories about a rigorous thinker in such a universe working out ways to exploit its ground rules.

I'm not sure exactly how much this would be a different from the regular Mage. As far as I understand, it's already all about exploiting the meta-reality thing using whatever trickery the mages come up with.

I'm not also so sure how doing the rationalist subversion would work in Mage, since its universe is a lot sophisticated about working in a nonrational way than regular naive fantasy works. You're basically up against an adult postmodernist instead of a child who believes in wizards.