Indeed. Almost meaningless. "Confirmed Coronavirus cases" is more a metric of the testing frequency than anything else. A better metric (but still not necessarily good) is the number of deaths in a village or region in comparison with the previous years
Other experts disagree. Yes, in many countries the confirmed cases are only a fraction of the total, but they are still useful. They show the trends, and the distribution. They show that New York City and Albany, Georgia are hot spots. They are only fraction of total cases, but they are probably a consistent fraction, in one country.
In Japan they are nearly 100%, because every patient goes to the hospital, even mild cases. Some people don't know they have it, but the government jumps through hoops to trace the known cases and find people who have mild cases. On the news every night they list all cases, and show how many cannot be traced (usually 4 or 5). In Korea, probably 90% or more are registered with public health agencies. In the U.S., no one knows, because we still do not have test kits or nurses to administer them. In Atlanta, people who are sick are told not to go to the hospital, because there is no room and if you are not infected, you may well be at the hospital.
When you have some idea what the ratio of confirmed cases is to total cases, you can draw conclusions. You can also combine this metric with others, such as "the number deaths in a region in previous years." Together, these combined methods give a reasonably clear picture of what is happening.
When you have no testing, no functioning public health system, no way to visit hospitals, and no government coordination, you might as well be back in the 14th century. That is more or less where we are in Atlanta, GA today. If you manage to get in the door at the hospital, you are back in the 21st century. Although, it may soon be the Northern Italian version of the 21st century, with 6% (??) case fatalities, given how many fat and unhealthy people there are in Atlanta, and how overcrowded our hospitals will be.
This epidemic can only be controlled when the public is educated, informed, generally in good health, and when it has faith in science and the medical establishment, and when it cooperates. That is the situation in Japan, and the government is doing all it can to keep things that way. There was a spike of about 200 new cases the other day, which put the fear of God into everyone. P.M. Abe who came on national news telling people not to relax, and that the country might still see explosive, uncontrolled growth "like Europe and the U.S." 40 of the cases originated in one hospital. That's good, because a pin-point source makes it easier to track down other people who may have been infected.
Unfortunately, the U.S. public does not meet any of those criteria; it is not educated, informed, healthy, and it has practically no knowledge or faith in science. The Italian public was also notably uncooperative until recently. People in Italy now say they deeply regret not taking this seriously, and not doing what the government recommended weeks ago.