Pot growers are rarely going to have any way scientific method for determining how much of any one cannabinoid is in their product. They’re just going to rely on taste, smell, and the “high” they get and try to select the best plants to make seeds from. They know generally about different plants from different regions and the properties of different types of marijuana like cannabis sativa, cannabis indica, or cannabis ruderalis, so they come up with the types of seeds they want to start with and cross the different varieties to try to come up with strains that have the properties they want. Still though, the basic make-up of the plants is the same. They all have the same cannabinoids, just in different concentrations. From what I understand for instance, Indicas are short stocky plants with shorter grower seasons. They’re the type generally found in Afghanistan and parts of Pakistan and India. A Colombian Sativa will be a much taller plant with long skinny leaves and a much longer growing season. Ruderalis are very short plants with almost no THC that grow really quickly and that do not require the days to get shorter before they will flower like Indica and Sativa do. The Indica’s are supposed to have high levels of THC and high levels of CBD and produce more of a “body high” compared to the more “cerebral high” of the Colombian Sativa that will have less THC overall but a much higher ratio of THC to CBD. A grower might cross the a Stativa and an Indica in hopes of coming up with a plant with the high THC levels of an Indica but the lower CBD levels of a Sativa, or a plant with a Sativa like high that grows short and stocky and quickly like an Indica. Most of the varieties they grow indoors are some type of Sativa/Indica blend. Some also try to breed in the autoflowering traits of the Ruderalis plants while still keeping the higher THC levels of the plants they are crossing the Ruderalis with.
This really isn’t any different than farmers crossing two types of tomato plants to come up with a new variety that has the better qualities of the original plants that they are trying to bring out in their new strain. They’re still going to get tomatoes. But if things work out for them maybe they’ll have the disease resistance they were trying to get from one plant along with the flavor and juiciness they wanted to save from the other plant, or the flavor they want from one with the early fruit set they get from another. Both farmers are going to keep growing successive crops, weeding out the bad plants and keeping the ones with the desirable properties to make seeds from, maybe backcrossing the plants from time to time to bring in traits they couldn’t get to hold in the new variety from the initial cross. Neither farmer is completely altering these plants such that he ends up with something totally chemically different than what he started with. The tomato grower will still have tomatoes and the pot grower will still have pot.
As I said, I’m not wading into the pot debate, Smoke, don’t smoke. It don’t know you, so it’s all the same to me. Do what you want.