Trading off efficiency for security is not wise unless you are in war. The same applies to supply chains.
Its not just war either, as the pandemic showed. Trade disputes that lead to sanctions, natural disasters, and lots of other things require the same security.
Its worth paying a bit more for the security, for the same reasons people buy insurance.
Yeah but this “ If you want security the concept of the mega city needs to be abandoned.” is not a bit more. It’s paying more for insurance than the asset insured. Perhaps you heard of the term over engineer or the cure is worse than the disease. I think it applies here as well.
Let alone all of the super expensive infrastructure that mega cities need, for example subways, buses, wide highways for traffic, heavy transportation for supply