That’s the bit I have no idea about. We don’t all get flu, despite there being no containment attempts.
Merkel said 80% of Germans will get it, but one German expert says it will be much lower.
The problem with the "We don't all get flu" position is that this isn't flu.
The normal flu that passes around has a level of societal immunity. So a large portion of society will be exposed to the virus but will not actually get any symptoms or become contagious. We also have annual flu shots to immunise vulnerable people.
With Covid-19, very very few people will have developed an immunity to it, and there is no vacination to immunise the most vulnerable in society. Society as a whole does not have the built-up immunity to it and so it is likely to pass from person to person to person and thus on to someone who is really vulnerable far more freely than regular influenza.
Mortality rates are only a small part of the story compared to contangion and immunity rates. If as appears to be happening, you can be contagious during the incubation period, before displaying symptoms then there is a positive feedback loop that will cause the expontial increases we are seeing in countries still sticking to the 'contain' strategy. You can only contain it if you remain ahead of the curve, catching an isolating people before they pass it on. Once you are behind the curve you need to immediately move to the delay phase to keep it from getting out of hand. That means reducing social contact to the bare minimum, so that clusters can quickly be identified and isolated before they pass it on to others. Once your recovery rates start to pick-up it is an indication that we are starting to develop societal immunity, and some of the restrictions can gradually be lifted.