You’re trying to translate too much between two countries in wildly different stages of a virus outbreak. While China’s numbers have its number of active cases dwindling, Italy’s in the early stages of its outbreak; the number of cases is probably strongly focused toward symptomatic and especially the worse symptomatic cases. As of now, Italy doesn’t even intend on testing people going forward who may have been exposed but are not showing symptoms. With time, the fatality rate will probably be lower than what it is based on those highly fluid numbers in the early stages, and almost certainly lower than the 5% you quoted from God-knows-where earlier.
As for China’s numbers, unless and until I see hard numbers from an external, reliable source, rather than aimless speculation that it’s far worse than China’s numbers show, I’m going with the best (essentially only) data available for the country that has had nearly 95% of the confirmed cases up to this point. Would I love for there to be independent data out of China? Sure! But there’s not, and I’m not about to start pulling numbers out of a hat.