I think that empty individualism is probably the most accurate model of identity at a metaphysical level, and so in theory, all things being equal, it doesn’t matter where in space or time an experience is occurring. I also think that, in practice, this perspective can potentially lead to more empathy for others because we see that we are all literally variations on the same theme, changing over time. But there are other key considerations. Most importantly, I think, experiences occur within brains that are strongly hard-wired to believe in closed individualism and continuity in personal identity, and this dramatically affects how we perceive our own suffering, including the feeling of helplessness, as you say. Even if we view our identity as formally disappearing from one instant to another, there is still continuity in the patterns and the memories, and there are reflections about the suffering, all of which affect subsequent experiences and can create downstream suffering. Most of these considerations are applicable to non-human animals as well. And finally, the ethical framework we use for society would be unworkable if it strongly conflicted with our intuitions, such as that it is wrong to intentionally concentrate suffering in a few individuals so that many others can enjoy happiness.