The numbers of people having the disease is certainly under reported, different countries are taking different approaches to testing and have different capacity. It also has a long incubation period, so there are a lot of infected people who are capable of passing it on but are currently showing no symptoms.
What we do know is that it is easy to transmit and (based on the official figures) is serious in about 10% of cases, requires hospital treatment (help breathing) in about 5% of cases and kills between 1-3%. It is more than capable of overwhelming hospitals in developed countries. Without drastic measures, it poses a very serious risk, not just to those who contract it but to people with other conditions that require hospital treatment but are unable to get it because hospitals are at breaking point.
Diseases come in waves, COVID-19 will pass the first wave in most western countries in the next four to six weeks. There will be subsequent waves, the worst probably happening next autumn/winter. Worldwide, it could kill millions.
I have seen no evidence that the symptoms are becoming less severe as it spreads.