1) Re: the story - I enjoyed the first two thirds of it, in a (pardon the expression) grim, dark sort of way, but I thought the last part, where our "hero" transitions into the realm of the Mapmaker and does his thing to be a little muddled. Had to listen twice to get a solid understanding. Interesting setting, but I also agree that the amount of world(s) was hard to justice to in a short story. I really like the Out-blade, though.
2) On the subject of "grimdark" - guess I'm not plugged in enough to have heard about this, but I can see where it comes from (I can also see where Abercrombie would want to "own" it, even tongue-in-cheek, given his recent dust-up on the subject on the subject of the dark screwed up protagonist).
I think, firstly it's an argument as old as Plato, and secondly it strikes to the root of why people read fiction - realism vs. idealism. We know full well there are awful people in the world who rape, steal, murder and (if possible) worse, and we know it's happened throughout human history, certainly in times of swords and doublets. But as story readers and listeners, we WANT our happy ending, our noble hero, our good guy who's selfless, who achieves the quest and saves the girl (boy is perfectly fine too). This is an old tension. On an emotional level, we want our fairy-tale ending, and "serious" authors (oh, let's say Abercrombie, Woodring Stover, and Martin) want to remind us that the world just doesn't work that way. I think the best example is very simple - in the original novel Game of Thrones, one lowborn fighter bests and kills a noble knight, and is then criticized for not "fighting with honor", and (quite rightly, IMHO) says "no, but he did".
It reminds me of a remark of Elliot Smith about how "if you grow up with yelling in your house, the last thing you want to do is make records with yelling" and it makes me wonder if the practictioners of "grimdark" - if there are any or if it's even a "thing" - didn't come from nice safe wholesome households and writing against that... or the fans thereof.
And of course there's nothing peculiar to Fantasy about this conflict - this is true in Science Fiction, and Westerns for that matter.