We decided to try an experiment for our current saga. We all like Mythic Europe, and I thought it would be fun to explore it through the eyes of a mundane, rather than through the regular perspective of a magus. Another player suggested that all the characters be Redcaps, working for the Order but ignorant of its exact magical formulas and powers. Some thought a typical companion might be too wimpy, so we opted to create mythic companions, a middle ground between my ultra-low fantasy idea and the usual fantastic nature of our sagas.
I had some ground rules. No one could have magic resistance of any type. The mythic companions had to be constructed by the rules in HoH:TL, meaning they have to have Blood of Heroes and a personality trait that the storyguide can "steal". Or, they had to use a mythic companion from another supplement. One player wanted to do more with faerie, and since the Realm of Faeries isn't out yet, we jury rigged some rules for him based on other mythic companion rules. Everyone should have a Supernatural Virtue or some mythical power derived from their bloodline, but no "super hero" effects: invisibility, flying, or teleporting. No one could be mock-Gifted, meaning no negative social modifiers that would keep them from interacting with mundane society.
We set the game in 1240, after the Albigensian Crusade and during the Medieval Inquisition. We also invented a catastrophic event in the Order's history that would warrant four or five Redcaps working together, rather than the single canonical traveler. Essentially, we took what we liked, ignored what we didn't need, and invented a background for the saga we wanted to play. That's what everyone does, right?
It's been about six months of regular weekly playing, and it's awesome. We've avoided the rapid power escalation that starting magi seem to always go through. Without magic resistance, our characters are susceptible to all sorts of minor mythical creatures. The Might 5 leprechaun with his annoying power to make a character dance really is annoying, not just another Perdo Vim target/trophy.
We like that our Supernatural Abilities work best out in the wild. We haven't changed the Realms Interaction Chart at all. We are at a disadvantage in town, which has become a role-playing advantage. We can't just entrance the local priest to do what we want him to, but now have to engage with him socially. Instead of seeing the Realms Interaction Chart as broken, I see it as helping to push weirdness (folks with supernatural powers) to the margins of society.
So, our saga might not be everyone's cup of tea, but we didn't make if for everyone; we made if for us. It has some very nice constraints that keep it low-powered (not necessarily low fantasy, as we've encountered several fantastical elements in the sessions). Abilities increase much slower than Arts, so while some characters might have awesome Supernatural Abilities, they aren't going to increase to god-like awesome anytime soon. And because they are Abilities, they are limited by a character's starting age. No Perdo 20 starting characters here! No Perdo at all, in fact. Not for everyone, again, but good for us.
So, in conclusion, we find that Supernatural Powers are nicely balanced as Abilities, with a nice starting range that allows us to affect stories but not, usually, to "derail the train" with them. The Realms Interaction Chart works just as well with them as with Arts, even better we think, since with Arts and maybe vis a magus could still hurl a fireball in a cathedral. That might be your Mythic Europe, which is fine, but it's not ours.