If you add up several thousand "rare" diseases you will find a few percent of the population affected. But the definition occurs at the disease level not the population level. CORD uses 1 in 12 to identify the population but 1 in 2,000 to define the disease. The EU uses the same parameter (1 in 2,000) but in the US, "rare" is defined as 1 in 1,500 people.

The definition of "rare" is not the issue. Finding the balance between the cost of developing an extraordinary drug and then pricing it so it is accessible is the story.