Whether and to what extent the survivors could catch up with the counterfactual universe strongly depends on the boundary conditions. Universe A could have expanded to other planets by the time B fully recovers. We are comparing the potential of a full, and fully developed humanity with a small post-apocalyptic fraction of humanity. I agree with you that planet boundaries (and other physical constraints) could reduce the potential of a random 1% in A with respect to B. But I suppose it can also go the other way: The survivors in B could produce less humans than any 1% of A, and keep this trend for many (even all) future generations. My intuition here is very limited.
Whether and to what extent the survivors could catch up with the counterfactual universe strongly depends on the boundary conditions. Universe A could have expanded to other planets by the time B fully recovers. We are comparing the potential of a full, and fully developed humanity with a small post-apocalyptic fraction of humanity. I agree with you that planet boundaries (and other physical constraints) could reduce the potential of a random 1% in A with respect to B. But I suppose it can also go the other way: The survivors in B could produce less humans than any 1% of A, and keep this trend for many (even all) future generations. My intuition here is very limited.