Strains are very real and the general concept exists in not only many other farmed plants as well, but domesticated animals, like dogs. All members of the same species, specifically bred for a certain phenotype through manual selection.

Now some people might say that X strain is good for sleep, Y strain is good for anxiety, Z strain is good for creativity, etc… That type of “phenotype” is much harder to quantify and I agree a lot of that type of stuff could be mumbo jumbo, though there could be something to it. But overall high THC strains (more stimulating) vs high CBD strains (more relaxing) have a clear difference.

However flavor is also a big differentiator among strains and that is much more easily quantifiable through the terpene/flavonoid profile, and plain old smelling and tasting. And people have been breeding plants for specific smells and tastes for thousands of years, so it’s not like this is some new concept specific to cannabis.