It comes down to how you view the opportunity
More seriously, teaching is usually the best way to learn.
I'm sure you know this given the ;-) but in case someone takes it the wrong way, although I speak at events even now that I'm not being paid a salary because I feel like it, very few things irk me more as analyst/consultant than someone who asks me to do something free "for the exposure."
Or, maybe what it's the best way to learn is how to make videos for Udemy. Not sure I think that has much value.
What I’m saying is that we generally don’t expect that part-time jobs get paid as much, in total, as full-time jobs. Someone working 1/4 time getting paid 1/4 what a full time person gets (maybe a little more - or a little less - for the flexibility and/or privilege) is normal.
So asking what fraction of their time Udemy instructors spend on Udemy tasks seems like a prerequisite for judging the fairness of their pay, and I don’t think this article covers that.
But I would assume a month of work would probably cover most new course content (and could be less)--given my experience in putting presentations together for conferences.
That said, given that assumption which I think is at least somewhere in the ballpark, typical revenues most seem to get don't really move the needle except as a very part-time hobby. Once upon a time I had a shareware business which brought in $7K/year for a bit but that only made financial sense in that it was something I enjoyed doing for a time and I walked away once I was sort of tired of it.
Both those numbers took me less than a minute to find.
[0] https://www.bls.gov/ooh/Education-Training-and-Library/Posts...
Paraphrasing Jeremy Irons’s character from Margin Call: “It’s a hell of a lot easier to be first.”