Hi Martin - before you go, you might consider joining the Medium Day coming up in August, and both sharing your concerns as well as learning how others have adapted.
Personally, I have seen my earnings more than double (from a low base) to several hundred dollars a month. This for writing about 2x week max.
The key is writing for an excellent publication and getting my stories boosted by them.
Because quantity has exploded on Medium, publications and boosting are two ways to help good writers rise to the top —and for readers to find them.
But you have to know how the system works. It has changed a lot, and it must keep evolving as it becomes more popular.
Good luck!
Tim