I also agree with everything you said previously. But I want to make it clear that the speed at which a writer produces a story shouldn't be a yardstick. Because whatever the job / work to be done in any field, it takes time and this time is due to experience (in the field in question) and to the vagaries of everyone's life. A novice writer will take much more than a week to create a story, and not a rushed story, but a story with tons of documentation to scrutinize, research on the theme of the story, on the scene. , the characters, cultures and people present in his universe for the stories of fantasy or science fiction, and then after all that, the writing of the story itself, without forgetting the proofreading and correction.
Just like a beginner draftsman will take hours to draw a simple cube in perspective, compared to an experienced draftsman. Both parties, as long as they are serious, have a tremendous job to do. And as you have already said, the motivation for the project cannot be the same for everyone, the imperatives of the personal life of each one, among others, can create many problems putting in danger the collaborations.
Otherwise sorry to sound Rabat-joie, but I wanted to clarify this point because it was not the first that I came across this kind of comparison.
p.s.: I answered like that because being a writer having trouble finishing writing his stories, I felt aimed ... it may be stupid of me but hey. And also, I have already had several bad experiences of collaboration where for one, it was me who had a problem and the other was my collaborator who did not want to continue our collaboration. Besides, I had to learn, and I'm still learning to write and draw, because I do my projects on my own.