If we reject either of these premises, we must also reject the overwhelming importance of shaping the far future.
Perhaps a nitpick (on a post that is otherwise very well done!), but as phrased this doesn’t appear true. Rejecting either of those premises only entails rejecting the overwhelming importance of populating the far future with lots of happy lives. You could still consider the far future overwhelmingly ethically important in that you want to prevent it from being worse than extinction, for example.
Perhaps a nitpick (on a post that is otherwise very well done!), but as phrased this doesn’t appear true. Rejecting either of those premises only entails rejecting the overwhelming importance of populating the far future with lots of happy lives. You could still consider the far future overwhelmingly ethically important in that you want to prevent it from being worse than extinction, for example.