Even in ideal conditions we don't have much impact on the lethality of the virus. If we are in a scenario where everyone gets infected lots of people are going to die. Medical care can change that by some percent but not enough to change it from "lots of people" dying. For example, something like 2/3s of patients that go on ventilators will die. Of the 1/3 that do survive a significant chunk, if not the majority, will have significant complications. They will live for another few months to a year with a poor quality of life before dying.

That might make you think a ventilator surge might save 10-20% of people who otherwise would have died. But that's not true because we can choose who gets the ventilators. The actual difference in death rate will be small because we will stop ventilating the cases that still have a 95%+ chance of dying even with ventilating. Ultimately, the impact of the ventilator surge is going to be a bunch of 80+ year old patients with significant comorbidities getting pointless interventions. It's going to save few lives and will only marginally impact the mortality rate.