You're not applying the logic all the way through.
If a great number of people are already infected and do not require hospitalization it grossly affects the math on the potential for overwhelming our medical system.
Those infected people unnoticeable to minor symptoms have the potential to be the herd immunity we'd want from a vaccine.
> All that is to say that the situation can only be worse than we already know. I'm not sure more data would lead us to isolate less at all.
More infected people who are unnoticed because they don't show severe symptoms and require hospitalization actually makes the situation better. It would lower the hospitalization rate and alter the projections drastically in the direction of less epidemic.
We are being cautious right now. That, by definition, means we're likely overreacting.