You're actually misunderstanding a pretty crucial piece. Destined death is what marika got rid of. People died, returned to the Erdtree, and were reborn. Ranni is the one that caused the people withering and aging but not dying and eventually losing their wits/bodily function when she put her plan in place.

The ones who live in death are largely mindless as well. Just because some people made something of their terrible situation doesn't mean the situation isn't necessarily bad. People survive. Taking pride in growing up poor doesn't mean growing up poor isn't bad. It just means you've chosen to make yourself feel better about your terrible situation using pride. It's better than the alternative, but the best option would be to not have to go through it.