Maybe some strains are more potent than the ones back in the 70s, but it can only ever be an assumption due to the absolutely huge amounts of strains that have ever existed with so many not being tested for THC content (which I hear is a quite complex procedure), many legendary strains are extinct now - apapulco gold, panama red, maui wowie, thai etc. and so many have never been tested...besides, increased strength means less needs to be smoked = better lung health