I completely agree, I've grown some killer shit from bag-weed (much higher quality than the bud it came off) SEEDS MATTER but keeping the plant healthy and happy matters too.No, it's not true.
Growing environment determines to what level the plant con fulfill its genetic potential. Only genetics can determine the potential growth of the plant.
Although to be fair, 75% of the shit weed out there is probably due to grower error, and bad seeds grown well will beat out poorly grown herb from the strongest strain.
So yea maybe sorta, but not really no.