My original point was that if creating people who are doomed to die of old age is okay, then creating people who die by whatever method of execution is convenient is okay. If both methods of death are the same, then this works. If old age is worse, the argument works better. As such, my original point still stands.

Also, with the exception of incredibly drawn out methods of dying (such as old age, chronic illness, and virtually nothing else), I don't think the pain of death is comparable to the opportunity cost of not living. As such, it doesn't really matter much which death is worse.