We’re already comparing to the default outcome in that we’re asking “what fraction of the default expected utility minus the worst comes from outcomes at least this good?”.
I think you’re proposing to replace “the worst” with “the default”, in which case we end up dividing by zero.
We could pick some other new reference point other than the worst, but different to the default expected utility. (But that does introduce the possibility of negative OP and still have sensitivity issues).
We’re already comparing to the default outcome in that we’re asking “what fraction of the default expected utility minus the worst comes from outcomes at least this good?”.
I think you’re proposing to replace “the worst” with “the default”, in which case we end up dividing by zero.
We could pick some other new reference point other than the worst, but different to the default expected utility. (But that does introduce the possibility of negative OP and still have sensitivity issues).