You're wrong, the statistics prove you wrong.
Alleria is in the Top characters in WOW Fanfiction, despite being the most "recent" character in that poll, since she was reintroduced in Legion and has had very little screentime since then. But she still appears in the same poll as Varian, Anduin, Jaina, Garrosh, and Sylvanas, who are absolute main characters of WoW.
If a given character is popular in fanfictions of a given fandom, then that means that the fandom likes the character and the character is popular, otherwise they wouldn't make so many fanfics about them.
Now if Alleria, with the total of 10 minutes of screentime across 3 expansions that she has, was able to appear in this list of the absolute most popular WOW characters in Fanfics, the characters who have the most fanfics, what does this tell you about Alleria's popularity?
The numbers have spoken and the numbers never lie.