Interestingly enough, the Ironsworn book seems to frame it a different way. Glancing through the section on fate moves, it almost always discusses solo/co-op first, then “guided play” (with a GM). The book dodges the question of which mode is the “default” mode. The book also states that while the GM can reference the fate moves (and if I GM’d this system, I would keep them in hand), that the GM “represents the whims of fate” and is “the oracle” in guided play.
So the short answer is: “replace” is a large word, but fate moves can play the same role as the GM. And in PbtA, the GM disclaims a lot of decision-making anyways, so it’s a blurred line.
The book does say that the GM can use and reference the fate moves. However, I’m not sure what you mean by confusing the GM’s position. As with any PbtA game, Ironsworn has its principles for how the GM should arbitrate play.
Disclaimer: I seem to be one of those gamers who aren’t perplexed by the “moves” terminology. With that in mind, let’s refer to how Ironsworn defines moves:
I’m on board with this definition. Moves as a self-contained system that resolves something. They have triggers; they have procedures such as simple if-then rules, dice rolls, or human choices; and they have effects. This works well with the conversation because the conversation also runs on cause-and-effect logic.
So while Ironsworn is using “moves” in the PbtA sense, I do grasp how Ironsworn is using the thing that it calls “moves.”
(God, this got longer than I thought.)