I am not understanding how those stats support your point. People are living longer with cystic fibrosis because of modern treatment techniques not because of a positive evolutionary change to their genome.

Yes with the principles of natural selection there is going to be a increase in the number of people with the cystic fibrosis gene since more are living to reproduce but as a result it leaves their decedents weaker not stronger genetically.

That was my point exactly. The multiple mutations of the same gene that lead to conditions such as cystic fibrosis are not neutral. They cause an alteration on the phenotype (the condition). If it were not for the advances in medical science, as the stats show with life expentacy at 14 in the 80s, such mutated genomes would hardly be able to reproduce. Hence, natural selection would (in a great enough generation span) take care of it. In the end it's a numbers game influenced by factors we don't clearly understand, yet.

“So on the one hand you can have identical genes leading to very different phenotypes, and on the other you can have dissimilar genes producing exactly the same”
― Eva Jablonka, Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life