who cares
Ppl use hub dynos as they are a more accurate and consistant chassis dynamometers at measuring power at the wheels, since wheel diameter, tire pressure, and tire slip or bounce off a roller plays no factor in the measurement of power at the wheels - the dyno is a tuning tool remember so consistancy important. They will read higher than a roller and this differnece increases with power output. However Iits unrealistic to think this reading is 25% because of the dyno type at these power levels, most likely do to something else.
250 on 8psi psi...yeah I would expect more like 210-20 myself with this setup.