I think the logical conclusion of your argument is that people in cities should not undertake any preparedness measures. I do not subscribe to that belief, and think it is an abdication of responsibility. It’s much more likely that I will need water/food due to supply interruptions than I will need water/food due to supply interruptions and also be subject to marauding gangs of thieves.
Also, where I live in the winter, it is normal to have a non-trivial amount of weapons in one’s own home, and something like 50% of homes do, despite being a reasonably big city by local standards.
I envision places like that to remain a lot calmer and more civilized longer than most other urban centers, where the means to keep order is a lot more centralized, and probably the first to abandon their posts in times of extreme crisis such as you allude to.