Schaffer thinks that pluralism entails atomism. This is because he assumes that there should be a grounding - things are not ungrounded, there should be an end to grounding, there are archés. In fact, the debate about monism too often takes archés for granted. It is as if there is no other options but some sort of creationism applied to grounding. In any case, if grounding is assumed,
pluralism entails atomism.
Schaffer's argument against pluralism is that it is possible that the world is gunky - everything has parts. Everything is infinitely divisible. In this case, monism would still make sense, but not pluralism. Bohn replies that it is possible that the world is junky - everything is a part. In this case, monism (there is a prior whole - priority monism - or there is only the whole - existence monism) is impossible. If the world is junky pluralism but not monism is possible.
I believe the world is gunky and junky. It is a consequence of the ontology of fragments, and of generalized Darwinism. There is no creation ex-nihilo, not even in the plural. It follows that there is only recombination. The issue seems really to be the arché assumption. I think it is better to refuse thoroughly this assumption.