highly fit individual doesn’t simply compete to reproduce within its own generation, but also with its children, and then its grandchildren, great-grandchildren, and so on,
This competition happens in nature too, especially in species which can also reproduce asexually. Cloning might as well be immortality.
You don't need to be immortal to compete intergenerationally. Even mammals do it.
Mortality is an important part of selection. Producing fit offspring is part of the game - a mutation that is good for you can be fatal for your offspring - see sickle cell anemia.
In this example, the children of exact-matching algorithms might all be worse than the parent because that's a daft approach, so you need it to die out to make room for other approaches.
