>>8150526 (lb)
you have a point
but you are not stating it correctly
cannabis has a range of active "cannabinoids" along with the infamous delta 9 THC (tetra hydro cannabinol) are many cannabinols, cannabidiols and other molecules that help balance out the effects of using that particular strain of weed. that's why some will wake you up, some will relax you and put you to sleep, make you laugh or give you the munchies, different weed strains have different effects
when the breeders select for one specific molecule (THC usually) they lose some of the others that help balance out the effect
so, the THC isn't "more potent"
the weed just has more of one specific component or another and less of the overall balance the older more heirloom weeds have