The Narration supports great man theory, one of the spiels the narrator tells you like 4 times says "history is the collection of the actions of great men", that's why the show is named that, the title itself is a play on this.
However the claim that it supports it and it is reactionary are two different ones, the guy in the other article is right. Mainly, in that the show does seem to imply that history as told by the narrator is warped, and that Reinhard is not necessarily a conservative. mostly, it seems the actual ideology of the show is somewhere between liberal and dengeist (a progressive figure that abolishes the aristocracy makes economic reform, and creates a progressive authoritarian regime in a Japanese show just reeks of dengeist to me).
What I think would be more interesting to think about is this, if the show implies the narrator is telling you his version, then from that version, what would be the actual story of the world? Now that's a real story worthy of being written