I've often wondered, with a cohort (community/society) of people who do not discourage freedom of expression, how many great works would come to fruition, but instead one is held back and then set free by drugs...?
I'm not sure it's the amount they drink, but the basic metabolic reality of aging. Everyone starts to feel it in their 30s and 40s. These writers just choose to keep drinking well past when anyone else would have slowed down or quit.
I feel like it's probably their lifestyles were not flexible enough to accommodate that kind of change without losing out on opportunities. The fear of death and stress of that life would make anyone work harder.
New drugs enhance. If you can get your hands on a chemical that invokes an altered state no previous artist has experienced then you're in undiscovered country.
Ken Kesey was a guinea pig in the CIA's early experiments with LSD. He went on to be amongst LSDs earliest recreational users, and that led to "One Flew Over the Cuckoo's Nest", which is a strikingly original and lucid novel.