I didn't say DMD was easier. You started with the broad generalization that rare disease was harder, when it's really not. It may be harder than me too drugs, but not than 1st in class drugs in multicausal diseases.
As an investor I like rare disease companies because it's faster, cheaper with higher rate of success. As a citizen, I'm not happy with the pricing model because they can't use the same argument about long dev times, cost of R&D, cost of failures as companies going after bigger diseases that take longer, much more expensive to get to market and 9/10 fail.
What's the rationale for charging $400k/yr for the rest of a kids life? People are complaining about solvadi costing 80k for a one time cure. How about 400k x 50 yrs= 20M for a non-cure?