From which verses did you derive that doctrine?
It does represent a corpse - a spiritual corpse. There were other words God could have used instead but He specifically chose to use dead - He knows what dead means.
Separation from God IS death in its fulness.
Look at Eph 2: 1,5. Do you see that the spiritual corpses (the dead) were not able to contribute anything to being made alive? Nope, they didn't and couldn't. If they could have, that would have been included, but since it was only by God, means they were dead, and as dead incapable of contributing to the process of being made alive.
The verses I provided depict the nature of death, that, for death to be death, it cannot be partial death: the dead are either fully dead, or they are not dead, there is nothing in between.