The follower counts on Medium are often greatly exaggerated, as I demonstrated in an article (link below). There are evidently bots flying around that boost the counts for certain writers (including me). I have six thousand followers, for example, and some of my articles fly under the radar with hardly any likes or views. The Algorithm rules all.
I’d estimate that some ninety percent of the followers of anyone with over a thousand followers are bogus or at least only superficially interested in that content. Wildfire, then, may have only several thousand serious, regular readers. They happen to be enthusiastic not because she’s especially talented but because she’s leading a fad and because there are network effects at play, so those readers tend to clap a lot for her work.
As to who she really is, the simplest explanation is that she writes under an alias to give herself more creative freedom. Readers might well be intrigued by the identity of their favourite writer, but she’s under no obligation to divulge personal information. The more critical and objective the writer’s output, the less relevant is that biographical information.
As to whether dark, pessimistic writing is especially popular on Medium, that’s ludicrous. Wildfire and Umair Haque are exceptions that prove the opposite rule, which is that most young, neoliberal readers—who go back and forth between reading on Medium and consuming content on YouTube, Instagram, or Pornhub—want to be uplifted. That’s why the most popular genres here are self-improvement, startup, and tech reviews, not philosophy or social criticism.