On p. 395 I do concede that the scale of deep history will add something to the problem if the life of the average animal adds more bad than good to the world. So, that is something defenders of the problem of scale could try to establish to keep using the problem. Here’s what I say:
One way of changing this equation would be to assume that the creation of each mortal creature on average adds more bad than good to the world. In that case, adding more creatures would make the world a worse place, and our world with its billions of creatures is a very bad place indeed. But then it would seem that God’s goodness is incompatible with creating even one mortal creature capable of suffering, and we would have plenty of evidence against theism regardless of evolution. This view of the world would also lead to a kind of problem of evil for atheists, as noted by Nagasawa, and to antinatalism, for then our parents would probably also have been unjustified in giving life to us, and we ourselves should also avoid procreating.
To clarify a potential misunderstanding, I do not mean to argue that the existence of additional goods in a larger world itself justifies the increased amount of evils. I am simply pointing out that the overall proportion of suffering in the world is the relevant factor for determining the severity of the problem, rather than the scale of the world. Defending the problem of scale would require showing why the same logic would not also lead to the (absurd) conclusion that a hundred-creature world is better than one with a million, due to the lower absolute amount of suffering. I am also arguing for reorienting the discussion to focus on the problem of the mortality and suffering of individual creatures, and whether God is justified in creating even one such creature. Due to the principle of repeatability of reasons, what is at issue is explaining types of suffering, and so the scale of evolutionary history does not add to the severity of the problem.
The point here is that we have to adopt an extremely bleak view of the life in order for the scale to make things worse, which would then make the problem of evil pretty darn bad even without the added scale. Moreover, the argument would anyway have to end up claiming that God’s creation of a smaller amount of creatures would also be unjustified / morally evil. Thus, even on such a bleak view of animal lives, it seems one should focus more on the type and proportion of suffering, before potentially moving on to the scale.
I also point out that such a bleak view seems to have large costs, as argued by Nagasawa. If animal lives on average really add more bad than good to the world, then could we reasonably have any admiration for nature, or existential optimism without contradiction? Should we work towards sterilizing wild animals and ending all life on Earth, so this endless cycle of suffering could be brought to an end?
I don’t think animal lives are that bleak, though, and argue for this a bit in the paper, although it’s not the main focus. The references go into more detail. For those who want to read a very optimistic take of the issues, I recommend Jon Garvey’s book God’s Good Earth (2019). Garvey argues, among other things, that an evolutionary understanding actually gives little reason to think that animal lives are full of pain and suffering, because there would be little selective advantage to that.