Is the harmfulness of death ante-mortem or post-mortem? If death harms a person in virtue of what it deprives a person of, then death would not harm a person whose life is not going particularly well.
So, Ralph's life is not going particularly well. It's just boring. Well, is it not obvious that he nevertheless has instrumental reason not to kill himself? None of us - surely - would recommend suicide to him. On the contrary, we'd encourage him not to take the exit. So, in reality we all recognize that even those whose lives are not going particularly well have instrumental reason to stay.
Now, a deprivation account of the harmfulness of death can't make sense of that. Ralph's death would not deprive Ralph of anything positively worth having.
So, join the dots. If Ralph's death will be very harmful to him - and it will be, else why does he have instrumental reason to avoid it? - yet will not deprive him of anything worth having, then the harmfulness of death must lie elsewhere.
Added to which, it is hard to see how one can be deprived of something if one does not exist. So, in order for death to harm a person by depriving them of something, they would need to exist.
So deprivation accounts of the harmfulness of death are in double trouble. They're of questionable coherence, given that it is arguable incoherent to suppose that someone who no longer exists can be deprived of something. But even if they are coherent, they are clearly inadequate, as they deliver the verdict that Ralph above is not harmed by dying, yet manifestly he is.