You also have to add all the other patologies that will get affected by the lack of ICUs. All in all, 10% is a safe estimate. That's why flattening the curve is extremely important. The actual percentage in need of ICU will surely vary with time, but that's the important metric, because that's how many people will die when the health system saturates.

Moreover, deaths from lack of capacity will not be limited to covid cases. And many of the current non-covid icu cases may be exposed to medical staff who are not being tested (in the USA) and die that way. This is what happens in nursing facilities like Seattle.