But there's a difference between a game that has some rules clearly spelled out and games that are more narrative (?), right? One of the issues that people seem to have with D&D is that it's clearly spelled out that you take 1d6 points of bludgeoning damage per 10 feet you fall, but when it comes to other situations the DM just makes a ruling. For some people that means the rules are incomplete and people have to "design their own game".
Well, I'm not sure that narrative and 'incomplete rules' are synonymous. There are a wide variety of games falling under this rubric. Some, like Burning Wheel, have very elaborate and complex rules! Played in a certain way, 4th Edition D&D is a quite narrative game, and yet it has quite detailed rules for a lot of things (though I admit, some of those are in tension with narrative play at times). I agree that narrative games tend to be more concerned with outcomes than with situation and process. So the Fate example where falling could generate a number of mechanical outcomes is true, the outcome "you suffered a falling injury" is more significant than the idea that the fall was a certain distance, which would be the overriding concern in D&D. It isn't that the game is incomplete, it is that the game is about "how does a character cope with a broken arm?" vs "you are now short some hit points, what do you do about it?" This is also why things like Magic are likely to be less codified in many narrative games. D&D can simply have 'cure light wounds', whatever the injury was, its fixed now. Fate might be coupled with a magic system where the characters need to do a ritual, with some sort of story cost, to heal a broken arm, and maybe they choose not to! Casting CLW is pretty much just SoP, if you're choosing not to its merely a resource allocation decision. One game is not 'more complete' than the other, it is just focused on a DIFFERENT THING.
But in Fate the consequences of falling are always a decision/ruling by the DM. The nature and extent of that ruling may be prescribed by the game rules, but I would say that in most cases DMs are going to be effectively limited to results of their ruling in D&D as well. It may not be explicitly spelled out in the same way as other games, but the social contract is the only thing binding at the table anyway.
Well, as certain people have argued endlessly here, rules tend to bind game participants, though they are not literally obligated to follow them. So, isn't it likely that, in a D&D game, where the 30' fall killed the fighter, that the almost trivial nature of the incident and interest in the fighter's ongoing story arc are of no consequence in this decision? While in a Fate game, the 'same' character might suffer an injury which then bears on some other element of their story arc, but an NPC might crash to the bottom of the pit and lie stone cold dead as a matter of course. So, yeah, the people playing each game are equally bound. the results of play of each game will simply be different, and they each have a different agenda. Neither is particularly arbitrary, one might see the fact that 3d6 yielded 11 instead of 10 dictating fighter death in D&D as pretty arbitrary, and likewise that the GM deemed the Fate fighter's story to need further development could be thought arbitrary, but both follow rules.
In D&D 3.x (and in a different way 4E) the designers did try to lock down the rules, in 5E they left more openings for the DM and group to decide how to implement things. So when I'm speaking of open ended, everything is on a spectrum. It's just ... interesting that some people who complain loudest about 5E's design direction simultaneously praise games that rely far more on GM (and possibly player, depending on the game) discretion and on-the-spot rulings.
4e is built, however, on 'exception based design' which allows for any needed elaboration of, or replacement to, any specific part of the rules whenever required. So it is really no less flexible than any other RPG. In fact I don't think it even has more rules than 5e, particularly (more material, but in terms of rules structure the two games are pretty comparable).