Those you describe would probably have been the same type of people regardless of their use of pot in my experience.
You may know losers like the ones you describe, but I know users who would burn through an unbelievable amount of pot on a daily basis and still were motivated, intelligent, and productive people.
Your stereotype simply fails to accurately depict the majority of heavy pot smokers I've personally known over the last 30+ years. It may accurately describe your observations, but I was very close to those I am describing and understand them very well along with what other recreational drugs they imbibed in their adulthood, and I don't know if you're as intimately familiar with the people you describe, so I can't say that our observations are comparable.
“I did my smoking from the 80s forward”
How old were you when you started smoking every day? Did you start smoking in the morning and continue to get high and stay high most of the day?