I get what you’re saying - but this is not practically true. Weed that contains 35% THC has a lot to do with the conditions it’s grown in which affects a lot of the other physical qualities of the weed. Smell, color, size of nug, density, humidity all are very correlated with potency.
Alternate take, dispensaries have enabled many people I know to get a reliable product that acts the same each time they buy it and use it, and let them dial in exactly what strain and quantity and method of ingestion works best for them. Before the commercialization one never had the diversity and reliability of product they have now.
Contrast that to the before times where people, as you put it, bought whatever the dealer was selling.
Density is just a measure of humidity in practice and thus pick date.