I really don't think this was a petition or prayer for groceries. The Greek language could easily have expressed this as something other than Epiousios.
Ousios is translated as substance or more accurately in English as Accident. As used in philosophy, an accident is an attribute which may or may not belong to a subject, without affecting its essence. St. Jerome translated Epiousios as "panem supersubstantialem", or supersubstantial bread.
Why not both? Isn’t God one Who provides daily bread - literally in the case of the Exodus?