FWIW, I lean toward believing the Thermian Argument being something very different than how people typically use the term.
In the real world, I sometimes encounter people who are making decisions based upon some version of "alternative facts" and buying into some fiction they've based their lives around. That (to me) is a Thermian Argument.
In the case of establishing logical validity in a hypothetical fantasy world, there is value in acknowledging that things work differently. That's kinda the whole idea behind speculative fiction, fantasy, and the pieces of literary culture and gaming which evolved into rpgs.
I certainly am someone who wants some amount of reality in my fantasy, so I do acknowledge overlap between real world influences and fantasy works created by authors living in the real world. But to claim there is logical fallacy in saying a world would function differently if built from "realities," physics, and natural forces not found in our own world is weird to me.