3711 passengers and crew on board total. 709 tested positive for COVID-19. So sub 1% mortality for the infected. And that's in a population that's likely much older and less fit or healthy than the rest of us. And in pretty ideal conditions for the virus to spread (close quarters, shared living spaces etc).
Also there are a lot of people who are "recovered" and tested negative, but a few days later were testing positive again. Either the testing kits are testing for the wrong things or are defective in some way, or there is the possibility the disease is biphasal or/and retreats to a reservoir in the body.
Either way, I think any hope of containing and exterminating the virus is long gone. We will likely all get this eventually. The question is whether we can manage that process so that hospitals are not overrun by the people who need inpatient care.
But the most salient factor of the Diamond Princess is this: everyone did receive top-notch treatment, and no healthcare system was put under strain by treating the patients. That will be hard in the real world, as opposed to the petri dish case.
The key thing right now is slowing down the spread as much as possible, so the medical system doesn't end up overloaded.
It seems to me that we will all eventually get this virus. It's on all continents, it's infectious and hard to diagnose before it's spread. So the question is whether we can manage it so it hits slowly enough that everyone who needs inpatient care can get it. I wonder how tmit will look when it hits western countries in full. I hope its OK.
https://www.worldometers.info/coronavirus/#countries