You could make some of the same arguments about animals that die immediately after mating or giving birth (e.g. they could have more kids too). Clearly that doesn't save them.
You seem to be tightly focusing on a possible reading† of the second-to-last sentence of my comment. I'm not sure why. It doesn't matter if older people have zero evolutionary benefit or simply less evolutionary benefit — the point is that evolution does not necessarily optimize for longevity (certainly not to the point where we can't do better than simply looking at how our basic instincts).
† I actually anticipated a response like this, which is why I added "clear." The evolutionary benefit of a grandparent is a lot less clear-cut and immediate than the benefit of a parent. Clearly I still did not communicate that well enough.
It still seems to me that this is all a red herring, and you're ignoring the overall thrust of my comments to argue with a point I did not even really make. As I said, whether grandparents offer zero evolutionary benefit or simply less evolutionary benefit than immediate parents is immaterial.
My point is that nobody has yet presented enough evidence to argue that simply "listening to our bodies" rather than taking any proactive measures is the best path to longevity. The view that evolution has given us natural lifespans that are as long as can be doesn't seem to be supported by the evidence.
