Thanks for linking to that research by Laura Duffy, that’s really interesting. It would have been relevant for the authors of the current article as well.
According to their analysis, spending on conservative existential risk interventions are cost competitive (within an order of magnitude) to spending on AMF. Further, compared to plausible less conservative existential risk interventions, AMF is “probably” an order of magnitude less cost-effective. Under Rethink Priorities’ estimates for welfare ranges, for cage-free campaigns and the hypothetical shrimp welfare intervention, existential risk interventions are either cost competitive, or an order of magnitude less cost-effective.
I think that actually gives some reasonable weight to the idea that existential risk can be justified without reference to the far future. Duffy used a timeline of <200 years and even then a case can be made that interventions focussing on existential risk should be prioritised. At the very least it adds level of uncertainty about the relevance of the far future in moral-decision making.
According to the authors of the linked article, longtermists have not convincingly shown that taking the far future in account impacts decision-making in practice. Their claim is that the burden of proof here lies for the longtermist. If the far future is important for moral decision-making then this claim needs to be justified. A surface level justification that people in the far future would want to be alive, is equally justified by reference to the near future.
You linked a quantitative attempt at answering the question of whether focus on existential risk requires priority if we consider <200 years, and the answer appears to be in the affirmative (depending on weightings). Is there a corresponding attempt at making this case using the far future as a reference point?
In order to provide a justification for preventative x-risk policies with reference to their impact on the far future we would need to compare it with the impact of other focus areas and how they would influence the far future. That is in part where the ‘We Are Not in a Position to Predict the Best Actions for the Far Future’ claim fits in because how are we supposed to do an analysis of the influence of any intervention (such as medical research, but including x-risk interventions) on people living millions of years into the future. It’s possible that if we did have that kind of predictive power, many other focus areas may turn out to be orders of magnitude more important than focus on existential risks.