I suspect that there may be a lack of agreement on the fundamental definition of 'Fiction First'. If you don't define it carefully, then EVERY RPG IN EXISTENCE has a play loop that starts with:
1. The GM says something about what pickle the PCs are in now.
2. ...
Step 1 is obviously FICTION, and it comes FIRST, so this must be a fiction first game! Right?
Now, as I understand it, Fiction First means that whatever the action/conflict resolution system is, it is fundamentally rooted in fiction. Thus in Dungeon World there is no combat system whatsoever. Players simply declare, in a fictional sense and with regard to the already declared fiction, what their character does. NOTHING WHATSOEVER can happen without a very explicit reference to and use of the fiction. Even in the thinnest case a player must describe his character as battling with the orc that's in his face. In fact, since there's no turn structure, the mere fact that he's NOW recounting what he's doing is already drawn from fictional considerations (IE whatever anyone else does must logically come later in time based on the GM's judgment of fictional position). Mechanics MAY then be invoked. This contrasts heavily with games which possess comprehensive combat systems where things like position, and what actions are available to the character, when they get used, etc. are all mechanically derived.