I have heard that weed from the 70s era only had ~2% THC where now at least dispensary grade can hit 20% to 25% THC. That could well be due to the drug war selecting for more powerful highs in smaller packages, but i would think that would also reduce the quantity needed to get the high you want.
Buy some CBD only bud and mix it with the THC bud for that old school experience. It’s pretty affordable and easy to do, assuming it’s legal (not sure how to go about it if your still buying from dealers).