If you compare the number of serious cases to the number of total cases for different countries you'll get a 10x difference. Norway tests more thoroughly then the other countries, so it has a huge number of active cases. But from those only ~2% serious. There may be different reasons for such a discrepancy but I tend to agree with your conclusion that we have a lot of asymptomatic cases around, higher then estimated R0 and lower then estimated fatality.
I came to similar conclusion just looking at the openly available numbers: https://www.worldometers.info/coronavirus/#countries
If you compare the number of serious cases to the number of total cases for different countries you'll get a 10x difference. Norway tests more thoroughly then the other countries, so it has a huge number of active cases. But from those only ~2% serious. There may be different reasons for such a discrepancy but I tend to agree with your conclusion that we have a lot of asymptomatic cases around, higher then estimated R0 and lower then estimated fatality.