Slow down there cowboy, you've got several things mixed up here:

1. The coronavirus is much more contagious and has a longer incubation period meaning that it takes longer for symptoms to show (if you played Plague Inc. then you know how valuable a long incubation period is.)
2. Influenza has a death rate of about 0.05-0.1% while the Coronavirus is between 2-5%. That is about 20-50 times more deadly than the seasonal flu which we are used to.
3. China is reacting this way because if this spreads throughout their country, a ton of people could die. That would be disastrous for their economy and standing on the world stage, so it is in their best interest to keep this virus as contained as possible.
4. If the coronavirus originated in somewhere like New York City, Boston, Chicago, LA, etc. then it would be just as bad. This isn't a disease that is killing people because of bad medical conditions. That is just the nature of the virus