Walter B. Gibson (who wrote many of the stories featuring The Shadow) boasted of cranking out up to 10,000 words per day.
He reportedly had typewriters in every room of his house, with a story in progress on each one.
In his peak year, he produced 1,680,000 words - roughly 24 full-length novels.
That was in the days of typewriters, snail mail, physical printing pressess, and truck distribution.
Putting something in the Kindle Store takes less than five minutes, and it's for sale world-wide within a day.
I'll bet Gibson could've churned out a quickie on the Maui fires within two days, if he'd had any way to get it on the market that fast.