I think CBD actually sorta fills up receptors and thus moderates the THC high. So the more CBD, the less high you can get on the THC.
Two strains that have 25% THC give you a different high? Why? Well it's the entourage effect. The terpene profile is what makes a strain unique. Different terpenes have different medicinal effects. This is why THC distillates all have the same buzz regardless of their source strain, all the other terpenes are removed leaving only the THC. THC and CBD are diterpenes, there are terpenes that we don't smell. There are companies that have analyzed the terpene profiles of different strains and have made products using terpenes from other sources to add to an extract to make it simulate a strain profile, often used in filling the vape pen cartridges.
So more than just CBD have an effect on the high.