Oh yeah, getting someone else to GM is always the best playtest method whenever possible. I'm going to try to run games of all the tf jam submissions, so I'll be sure to let you know how it goes.
Narrative freedom is important, but it feels strained because both the Beliefs and Monster Traits are points to keep track of, so to be mechanically grounded while narratively absent just makes them feel abandoned. I see easy fixes for that though, and this is a cool starting place with a lot of potential.