That seems to contradict the empirical outcome of COVID, where smaller nation-states (Denmark, Singapore, Taiwan, New Zealand, etc) were able to provide for their citizens much more adequately than larger counterparts.

I recommend listening to this podcast that outlines exactly why smaller polities were able to be nimbler: https://soundcloud.com/reuters/the-exchange-too-small-to-fai...

Yes, economies of scale provide advantages for procurement, but after a while, there are diminishing returns from more scale. That is to say, New Zealand's population is a sufficient scale, it need not pool its procurement operations with Australia. It's a key differentiator between Federalism and Individualism.