The key way you can earn through Medium blog is the Medium partner program. Authors receive payments in accordance to the time that paying members spend in reading their published content. The more appealing your articles, the more you earn. Others also use Medium to send traffic to their blog, product or service.
Assuming you joined Medium, would you be writing primarily to receive exposure and traffic or to immediately receive an income via the Partner Program?
The Medium Partner Program is clearly the main path, but I also think that consistency really matters. Most writers who habitually post, engage with their readers, and write about trending topics are usually better off. However, there is time factor involved too, meaning, it takes time to build a loyal audience and once you have it, the earnings become more stable.
Another method that people take advantage of Medium is the repurposing of contents. An example would be taking a significant portion of longer content and then linking them to the original website. That way, you're not going to depend on Medium payouts only, but also building an audience you fully own.