Lord of the Rings vs. Ring of Darkness

Perumov's works are all terribly primitive.

Examples? Does the multi-layered and intricate plot leave many questions unanswered until the very last pages of the Ordered Cycle? Does it involve merging several book series into one? Does it feature complex characters and the changing nature of many of them?

The Dark Circle is fan fiction.

In that case, "The Lord of the Rings" is fan fiction based on the Ring of the Nibelungs, and Goethe's "Faust" is fan fiction based on ancient Scandinavian sagas.

If you dared to mention in a serious RPG that Perumov is generally not bad, you would be buried alive, or at least sent to an asylum.

By "serious RPG," you probably mean a gathering of orthodox and fanatical Tolkien fans. Well, fanaticism usually doesn't lead to anything good. It's good that there are fewer of these "serious" RPGs and more RPGs with the participation of normal people with open minds.
Perumov's work has proven its viability, at least by the fact that it has been published for over ten years, has gathered its group of fans, and even in a dispute on Litforum between Tolkienists and Perumovists, the Perumovists won.

And Nienna's "creation" is just a bunch of sentimental female drivel spread over many pages.

Examples? Try writing a couple of pages of similar drivel that is also the opposite of the plot of a well-known book, but written logically and correctly, and with beautiful turns of phrase.
I know many jokes about Middle-earth myself.
Let me clarify: I am not a fan of Nienna (I only liked the first part of the Black Book of Arda), and I am not a fan of Perumov: I have already said that he has some flaws, the narrative is sometimes drawn out, etc., but you can't criticize them for "daring to touch the sacred."