"Only magical characters can be truly fantastic, but you can play a non-magical character" isn't the same thing as "a system that models Fafhrd, Conan and Pippin."
I think that you are conflating more than one meaning of "fantastic" here.
For the sake of discussion, I think we might consider coming up with some common definitions. "Mundane", as I am using it, means "not coming from a supernatural source". "Magical" means "coming from a supernatural source". I think we could add a working definition of "Fantastic" (in this context) as "Not considered likely or possible in the real world; that which would tend to confound belief if claimed for the real world".
By these definitions, this thread has already demonstrated (IMHO) that elements which some might find unlikely or impossible in the real world have, indeed, been part and parcel of the real world.
When I was a child, it was gospel that we would never find soft tissue from a dinosaur, never be able to detect extra-solar planets from our solar system, and never know what colour any part of a dinosaur was. Yet, all of these things have now come to pass, within a relatively short span of time.
So, what qualifies as "Fantastic" is, of course, based both upon the individual and the perspective of society at the time. I would agree that a system that models all three of the above must allow non-magical characters to be fantastic, if (and only if) one is prepared to also accept that the real world has contained (and likely contains right now) "Fantastic" people and events.
For you, perhaps, but I jumped into this part of the debate in response to some pretty black-and-white statements about what can, and what cannot, be done in a game.
What you go on to describe isn't a trope, but bad game design (i.e., game design that fails to live up to its goals). I am not going to comment on whether or not any particular game fails in the way you suggest, except to say that I think the claim (in general) exceeds the actual failure, IMHO and IME.
AFAICT, and IMHO, "I dislike games that promise X, but then fail to deliver on that promise" isn't a contentious statement, regardless of what X is. That hardly needs a rebuttal!
Personally, I think the trend to try and classify EVERYTHING as a trope is what needs to die.
Hear, hear!
RC