I think those statistics are extremely suspect. I subscribe to a few fiction authors on Patreon, and there's a few I did subscibe to but don't any more. I know of at least 4-5 fiction authors making a lot of money, like $10k+/mo ($15k+/mo in some cases) writing fairly niche content (litrpg and/or xianxia type work).
Then, when they get enough chapters for the current long-running fiction together, they bunfle it into a book and release on Kindle Unlimited, as an additional source of income.
Here's some examples:
- https://www.patreon.com/senescentsoul - 2163 patrons as of now, minimum tier is $2.50/mo, but I suspect most people are paying $5 since that gives access to all advance chapters and not just some, and you can read delayed chapters on royalroad.com. So, probably somewhere between $4k and $8k a month, and this is their side hustle while in college I think.
- https://www.patreon.com/DefianceNovels - 1393 Patrons. There is a $1/mo option, but various tiers from $3/mo to $10/mo give you up to 50 advance chapters from where it's publishes for free on royalroad.com.
- https://www.patreon.com/jdfister - Page says they are making $4,116/mo from 517 patrons, similar situation as above with royalroad.com and advance chapters, as a point towards how much to expect the above people are making.
- https://www.patreon.com/Zogarth - $12,753/mo from 1,886 subsribers. Same situation as above with free publishing on royalroad.com and advance chapters.
- https://www.patreon.com/RhaegarRRL - 3,317 patrons, my guess is they are making well above $5k/mo.
- https://www.patreon.com/Shirtaloon - $17,297 from 2,403 patrons. Similar as above. Books showing up on Kindle Unlimited.
These are just some people I actually read or read at some point in the past for a while, not a bunch I searched out that includes the top people. This is an answered question, IMO. If random web serials I'm reading are making this much money, I suspect there's a large amount of people making money this way.