It's not immediately clear to me which of these is actually more important, but it doesn't seem quite as simple as this article is portraying it to be.
> you have the power to enforce city-scale quarantines rather effectively.
These two things cannot possibly both be true, which is why people are skeptical that authoritarian regimes are good at this kind of thing. If you can't trust what your officials are telling you, you can't organize and maintain a quarantine, an effort that requires detailed coordination to keep the quarantined area well-supplied enough to avoid most escape attempts.
This is not to say that democracies are "good" at it, just that the idea that authoritarian regimes can actually control their people any more than democracies can is mostly a fantasy.
That's part of what contributed to various failures explored (I do not know how accurately) by the HBO Chernobyl series. Punish truth and reward lies, and you're bound to end up with fragile systems that can't be efficiently fixed or otherwise addressed when they fall apart, in part because information can't be trusted.
[EDIT] notably it also explores the benefits of authoritarianism: when The System finally decides people who can fix the problem should have what they need to fix it, by god, they'll get it.
https://www.motherjones.com/kevin-drum/2020/02/where-should-...
I suppose we can put them onto military bases.
Edit: Oh, you said city scale. Well, I’ll leave this up anyway.
Because decision making here is less centralized. People have rights, and they will agitate about them. It's not clear where the governmental authority to quarantine an entire city would come from in say, the US. It might be constitutionally challenged, people would get mad and sue. None of that happens in China.
Enforcing quarantine in New York would be very difficult, not least because it's in the middle of a continuous urban agglomeration between DC and Boston with no hard boundaries.
You now have a quarantine zone separating New York City, Long Island, and some of the nearby cities in New York from the rest of the country. The Hudson River provides a pretty decent barrier to travel along the NEC. The Delaware, Potomac, and Susquehanna also provides some barriers, but enforcing quarantine barriers to inland travel is much more difficult (unless you're cutting off the Delmarva entirely).