AbdulAlhazred
Legend
Here's the thing: In Dungeon World, what actually is the measure of the 'hardness' of a move? I mean, you have a loop where the players roll checks on 2d6 against whatever move they are making. There's no adjustments to this. DW doesn't have "DC" where when you fight a dragon you gotta roll a 20 to do anything against it! One move isn't 'harder' than another. GM moves are either 'soft' (IE they simply evolve the fiction and don't invoke a specific immediate threat) or they are 'hard' and they do. The former are setup moves, which allow the GM to build the tension. The hard moves then release it.You've failed to explain how my argument is "facile" in any bad way, so that's really just kind of a weird insult-y way of admitting I'm "technically correct, the best kind of correct".
Certainly you appeared to imply that there's some kind of mandate or principle to "swing for the fences" in all PtbA games, and I was being weird, but even a cursory examination of DW (which I have in front of me) shows that definitely isn't true there. And the range of moves you have is frequently extremely constrained.
As for "limited only by the fiction", well one good example in DW where I feel like you're demonstrably wrong is debilities. You can basically go wild inflicting them on PCs (nothing suggests otherwise), and equally you can do stuff like rip out people's hamstrings or chop off their arms and so on whilst staying within the fiction, and you going hog-wild on that is going to very rapidly see the adventurers all crippled or incapable, and unless they have the right magic, which they probably don't.
Also in the D&D-style settings "SURPRISE DRAGON" can be following the fiction (though at least in DW there's a decent chance they'll beat it). I can think of multiple D&D adventures featuring a "surprise dragon". Hell, Thunderspire Labyrinth, H2 for 4E, had one for example (a Green Dragon in a place that makes zero sense and where the attempted explanation for its presence does not at all make the situation better).
The only other element here in DW is resources. PCs have hit points, and they have various gear, coin, etc. They also have whatever fictional relationships and such exist for them, which are less formalized resources (IE your family, your town, your friends). The GM can threaten the later (or the former) and the resources can be expended, which is basically a soft move (often a consequence of a player move). These are just there to up the tension and maybe add to the fiction a bit. Really, about all the GM decides is hard vs soft (does Jason leap out at you, or do you hear some noise) and what resources have you still got (did you drop the knife when you ran or not).
Again, there's no 'difficulty' in PbtA game play. You aren't 'letting out all the stops' or 'going easy'. Every check has the same success threshold, no matter what. Everything that happens leads from one move and its check to the next. The fiction is what matters, the mechanics just tick along.