China didn't quarantine over a billion people. Even a communist government doesn't have that kind of power.
I don't mean that they literally quarantined the entire population, but they did implement draconian restrictions on a large part of the population.
I think it's fairly obvious that those measures are responsible for the decline in new infections.
What else would it be? There's no vaccine.
The mortality rate is nowhere near 3%.
Well, the figures you cited (80k infected, 3k dead) yield a mortality rate of 3.75%.
The estimates from academics that I've seen are around 2-3%, or about 10x the flu.
Another important distinction, perhaps the most important, is that a huge fraction of people who don't die still require hospitalization.
Hence the shortage of beds, ventilators, etc.
If we had enough supply to meet all of that demand, this might be much less serious, but we don't.
There are no hard statistics yet it's all too new but a fair estimate is more like .5% in people over 70 or with pre-existing conditions and just about nothing for healthy people.
Where do you get that figure?
You can't use the confirmed cases v. deaths for morbidity numbers because you don't know how many people are infected but not symptomatic or just had typical flu like symptoms and self medicated etc.
The same applies to the numerator.
Further, assuming both # infected and # dead are accurate (or equally inaccurate), the simple case fatality rate is going to be an
underestimate in an ongoing epidemic because of the long incubation period. That is, the number who die today should not be divided by the number infected today, but by the number infected some time in the past (i.e when the people now dying were infected, which is of course a smaller number).
Here's a recent article from The Lancet. They put the simple case fatility rate at 3.6% and the adjusted rate (as explained above) at 5.6%.
https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30195-X/fulltext
No one knows for sure, but I've not seen anything from any reputable source that isn't vastly higher than the flu.
It's a bit worse than seasonal flu but hardly ebola.
Ebola is well over 50%, so no, it's nothing like ebola, but it's also not the flu.