A healthcare system will typically have a good idea what it needs, whereas a pharmaceutical company will rightly enough focus on what will make the most profit.

Put another way: you don't need to set prizes for every drug. A better treatment for malaria is not going to make much money, because most of the patients will be in less-developed countries. But if you produce a side-effect free drug to reverse baldness, you will absolutely mint it by first selling into wealthier countries at very high prices to "skim the market", then lowering it over time.

Prizes would work better for low-profit/high-impact, for the rest you can mostly rely on pharmaceutical companies to rationally pursue their best interests.