The crowding can cause a lot of morbidity before anyone knows what's going on or how to treat the new infection. This is what happened in New York, the pandemic ripped through nursing facilities killing thousands of seniors well before any treatment was available.
If things unfold more slowly, you have more time to develop treatments. A lot of the deaths in NYC occurred before we figured out that just laying people on their sides reduced the risk of dying significantly.
Moreover, now that we have the ability to rapidly produce vaccines, it isn't a forgone conclusion that everyone will necessarily "get the virus eventually anyway."
If things unfold more slowly, you have more time to develop treatments. A lot of the deaths in NYC occurred before we figured out that just laying people on their sides reduced the risk of dying significantly.
Moreover, now that we have the ability to rapidly produce vaccines, it isn't a forgone conclusion that everyone will necessarily "get the virus eventually anyway."