Excellent article, and I think "historical fanfiction" is an excellent and appropriate term for alternate history, especially internet alternate history. I could repeat yet again how a lot of stuff (and not just the subject of this article) that could easily be considered AH just isn't labeled as such because there's no real incentive to do so.
I think that the term "alternate history" itself can be at fault here, because it can be too vague and too specific. On the too vague end, there's how you can consider any type of fiction that isn't a specific, trying-its-best-to-be-accurate reenactment to be "alternate history". On the too-specific end, there's the dominant Turtledove/High Castle-esque story with huge, blunt obvious divergences (ie, Axis/Confederate victory) that's prominent enough that people see that when they think of alternate history and not anything even slightly more subtle.
And there's a further "issue" (although that might not be the right word because it sounds more negative than it is) that a lot of people with tastes for one type of alternate history won't care for another type just because it's in the past with a divergence. I'm highly skeptical that there's a lot of overlap between the conniseuers of 18th-century divergence historical romances and those of say, Harvey Black's "Effect" series of World War IIIs. And if there was, it'd be probably just due to enjoying different types of stories on their terms rather than some "a-ha, they're both alternate history" feeling.
(Sorry if this sounds like I'm rambling, it's just I've gotten a fascination for looking at these niche fandoms since I realized how small and disconnected from historical/cheap thriller fiction in general the "conventional WW3" subgenre was).