The quantity of a particular species in an ecosystem has an equilibrium point. The optimal amount of a particular species is a number.
If there's no death, this number will be pushed out of equilibrium, and the given species isn't dedicating its niche in the ecosystem to the most superior 'version' of itself, therefore not investing the niche resources in the best bet of progressing the species.
This is more than speculation, how is this not beneficial?
Most death in those systems is due to predation though. Just look at what happens when natural predators are removed, the population explodes and then busts due to starvation. If your conjecture was correct then the population would self-regulate by aging and dieing before reaching that point.
It would simply take too many genetic changes in a too short period of time to change the aging rate to compensate for such a sudden change in the environment. Remember, genetic adaptation can take years, decades, or even centuries (think lactose intolerance which happens to be 1 gene).
This is more than speculation, how is this not beneficial?