Manbearcat
Legend
RE the bolded phrase:
No imaginary people exist, whether the game being played is trad D&D, or doctorbadwolf's D&D, or Dungeon World played as @Manbearcat does. That's inherent in them being imaginary.
On the other hand, just as in doctorbadwolf's D&D game the various participants imagine various character existing beyond the perception and interaction of the PCs, so do the participants in Manbearcat's DW game.
So the only relevant difference I can see in the neighbourhood of the bolded phrase is that Manbearcat decides what happens in the moment of play whereas doctorbadworld decides what happens in advance of the moment of play.
I don't see any particular reason to think that alignment is more helpful in the second rather than the first of those two approaches to play. I can decide in advance what a character will do without needing an alignment label.
The last time I GMed a game that uses alignment was 4e D&D. My approach to GMing was closer to Manbearcat's than doctorbadwolf's. I used the alignment labels to help me make decisions in the moment of play - eg if I though that a given moment of play would be enhanced by introducing a chaotic antagonist into the situation, I would use the alignment labels on the lists of candidate antagonists to help decide which one to use.
As Manbearcat has said, or at least implied, one consequence of this was that the game didn't focus much on interpersonal or character-focused drama of the sort he has described in his DW game. Rather, the focus tended to be on politics, history and cosmology. I think that's a natural direction for a game with D&D-type alignment to drift into. I would never think of using D&D-style alignment in a game that I wanted to be character-focused or "close" and personal in the way that Manbearcat's DW game seems to be.
Consider your Paladin Thurgon of the Order of the Iron Tower vs @darkbard 's Paladin Alastor of the Fraternity of Truth.
* They're both of a Lawful and Good bent as orthodox D&D alignment would have it.
* They both belong to Order/Fraternity and are at/near the apex of the hierarchy.
* They both see providence in the world and act upon it.
* They both wear heavy armor and a shield.
However, there are distinct differences as well:
* While they also both confront hierarchical corruption, it is at opposite ends of the caste system (Thurgon a king and his chamberlain and Alastor a laborer and his employer). Its not clear to me that either would be involved/devoted to the other's causes if the situations were inverted.
* While its not clear to me how much Thurgon is emotionally volatile/vulnerable (it seems not much, though play never wandered inward with respect to Thurgon), the character of both Alastor's inward reflections/communion and his outward expressions of divine authority reveal a level of volatility/humility/vulnerability (though not a lack of outward conviction) that isn't Paladin SOP. I could see Alastor being a reformed alcoholic/addict whose nature is entirely "un-Paladiney" and he fights tooth and nail every day to sustain. Meanwhile, Thurgon was lucky enough to be born the rock that the tide breaks upon.
* In our play, Thurgon's Order was already accepting of female Knights. Perhaps it was always this way or perhaps Thurgon only recently propelled this change. Meanwhile the legacy of Alastor's order is the inverse (exclusively males) and he is taking it on providence that it is his place to change this. Its unclear if this will work or not (it may fail dramatically...the next several sessions will sort that out).
The point is, there are many, many conceptions and manifestations of a Paladin. There is ample drift/divergence (both outwardly and inwardly) between Thurgon and Alastor (and surely more still tha I've noted above) that are at tension with the homogeneity expressed in Law and God discretely and especially the expectations that arise from the intersection of those two.
D&D culture has this tendency toward "Paladin homegeneity", when in reality, (a) THAT SUCKS AND IS BORING, (b) that isn't how people are (in genre or reality), and (c) actual compelling Paladin play rests upon BOTH the genre conceits of Paladinhood AND the struggles of a human (or whatever) aspiring to meet an impossible purity test.