I think there is a lot of efficacy left on the table with modern studies, clinical trials, and drug development. Most of the work is looking for treatments that work for the majority of the population. If a treatment was effective than standard care for 10% of people, it would be discarded.

It is more economical to start over looking for something that works for 90% of people.

Drugs an treatments aren't evaluated and discarded when proven worthless. The bottleneck is the number of treatments in development, so they are discarded when something else has a better ROI.