@Mata’i Souchon, I have updated this paragraph. I agree more actors would be responsible for the impact linked to AWF granting more to organisations as cost-effective as SWP (me, AWF, their donors, and the organisations) than to that linked to me donating more to such organisations (me, and the organisations). My counterfactual value, which was I estimated in my post, is the same in both cases, but my Shapley value, which is what matters, is larger in the latter.
I have reverted the changes regarding the Shapley value. Thinking more about it, I realised what matters is not the number of necessary actors, but whether their actions are sufficiently independent from my decision about the offer, which I think they are.
I have reverted the changes regarding the Shapley value. Thinking more about it, I realised what matters is not the number of necessary actors, but whether their actions are sufficiently independent from my decision about the offer, which I think they are.