If people there stopped all preventative measures, yes it would get much worse than 3x.
On the other hand, there's one very specific way that considering NYC gives us data we can't (yet) get elsewhere. While it's possible that we're underestimating disease prevalence by 50x elsewhere, it's basically impossible in NYC (almost 2% of people already have tested positive, with less than 10% of the population being tested).
Depends on whether mortality rates can be variant on environmental conditions, such as viral load, population density, access to healthcare/ICUs, population socio-demographic profile, etc.
What I would still say is that it's reasonable to say "NYC has .18% of its population dead. It's extremely implausible that this disease is no more lethal than the flu is, when that's 10x the overall death rate from the flu. If you present me evidence suggesting that from elsewhere, it's going to have to be quite strong to overcome the evidence from NYC."
edit: it shouldn't be controversial to say that a thing that kills 30-80k per year with active measures of mitigation already something that would be more deadly without a vaccine. seriously reflect on that. the corona virus is something we need to take 100% seriously but also acknowledge that the flu is also very deadly... even more so without any mitigation (thankfully we have for the common flu)
The flu as-is causes 45,000,000 sicknesses every year in the US alone.