Aspirin already exists and improvements to it are marginal.
This kind of extreme utilitarian approach seems flawed when you view healthcare as a human right. Reducing pain from 1.5 to 1.4 to millions of people is not really as valuable as saving one person's life. That's my opinion at least.
Of course, developing a drug that could save thousands of lives or one life is a real problem that governments and pharmaceutical companies need to face. And I would agree that in this case a utilitarian view is helpful.
But on the other hand, companies are not making these decisions based on ethical frameworks. They're making them on a basis of shareholder profit maximization. When you talk about "reducing the pain" do you actually care about reducing pain or is that simply a positive externality to the profits you'll make.