I don’t know, some of my most interesting art pieces have come about when I’ve been stoned. My sober ones always lack a certain pizazz. I’ve read through that research article I think you’re mentioning, the methodology seemed too small in scope to really capture a change in something intangible like creativity. I think a study that takes sober artists with zero drug experience, have them create something, spend a few months smoking weed, and then create something again would be more encompassing on THC’s affects on creativity.
Also I’d be curious to see how stress relief and a good mood affects creativity as well. Sure some art comes from dark places, but I’d imagine its easier to be creative when you’re in a good place mentally.