The problem there is that you're making the decision after the fact, rather than before the fact.
First you need to come up with your defining rationale for the reason we have a health care system. If it's not to maximize population health, that's fine. I'm an analyst and I'm an economist. We try to seek the best way to achieve the goals that people wish to achieve, given the need to make choices because of scarce resources. If you're looking to find another solution or another description of what the health care system should be producing, that's fine. You need to find out what that is.
No matter what you decide, you need to realize there's going to be a trade-off. If you're going to fund a drug that is not going to increase the overall health of the population, that's reasonable and that's okay, if that's your objective, but you need to define how much more value you put on funding treatments in one area versus another.
As I said earlier, lots of elements of society suggest the general public does not favour the idea of being biased in favour of one population group versus another. As a politician, you need to decide the purpose of having a public health care system. If it's not to maximize the overall health of the population, come up with some other objective, but don't say it is but you'd like to treat this other group differently, which will then not lead to that objective being obtained.