While I understand the facetiousness of your comment, I should take the opportunity to point out that there are medical strains that are bred (optimized) to treat certain specific conditions.
So, the fact that we have medical marijuana does let people create higher-quality (and higher-precision!) products, vis-a-vis available offerings on the black market.
My comment was not intended facetiously in any way.
Sure, while certainly the change in legal environment engendered all sorts of new breeding, by and large most medical marijuana is the exact same strains that were (and still are) sold on the illegal market, largely grown by the same people who would be/used to/are growing it for the illegal market.
So, the fact that we have medical marijuana does let people create higher-quality (and higher-precision!) products, vis-a-vis available offerings on the black market.