OK, so I started with 4e and really 'pulled it apart' and thought about all of this, and then redesigned it. My conclusion is that 4e has objective DCs. This is born out by all the reams of lists of such in the DMG! An iron door has a DC of X to break down, etc. Then there is a 'tag' attached to each such DC that is 'level', which tells you the level of PCs that this might be a moderate challenge for (exactly the same way level works for 4e monsters, BTW). Now, 4e isn't 100% consistent in labeling everything with a level, and maybe some adventures give different DCs for basically the same stuff, or whatever. Its not a perfect system and different GMs can subtly alter the flavor of the game by moving these DCs around a bit.To me, this seems to describe a framework of "objective" DCs - ie the DC is established by reference to how hard something is in the fiction, where that difficulty is conceived of in some "absolute" sense rather than relative to the person attempting it. So freehanding a sheerwall of volcanic glass is framed as very hard because that's what it is: and the fact that it's actually only moderately hard for the high level rogue (because the rogue is so skilled in freehand climbing) is not factored into the setting of the DC at all - the rogue's superior ability is all expressed, mechanically, on the PC build side which then yields a number applied to the d20 roll to see if the DC of 25 is achieved.
Games I think of that use this approach are Classic Traveller (without coming out and saying so; it's just absolutely taken for granted), AD&D (ditto as for Traveller) and Burning Wheel (which is very self-conscious about it and gives advice to the GM about how the setting of obstacles in this fashion is a key tool for establishing the feel of the setting; Burning Wheel factors in approach a bit differently from 5e, eg because skills figure differently in PC build and it has a different system for augments based on similar/complementary skills).
Games that I think of that don't use this approach are HeroQuest revised (difficulties are set based on pacing considerations - basically the more previous successes the higher the DC), Marvel Heroic/Cortex+ Heroic (all checks are opposed, either by another character whether PC or NPC, or by the Doom Pool) and Apocalypse World (there are no modifiers to moves for difficulty; that's all handled in framing and consequences).
4e is a bit of a mix but, in the end, I think closer to the second suite of games. In 4e difficulties do have an "objective" dimension in the sense that (say) Orcus has a higher AC than a kobold, and the DC to sneak past Orcus's silent watchers in Thanatos will be higher than the DC to sneak past a goblin sentry. But most of the time this "objective" aspect simply falls out of picking level appropriate DCs and doesn't need to be thought about case-by-case; and the skill challenge structure with its resultant closed-scene resolution also generates a "relative to" rather than "absolute/objective" dynamic to resolution.
When I designed HoML 1.0 I then simply built a chart, it shows LEVEL and DC, no 'easy', 'medium', 'hard', none of that stuff. Every level has an attached DC, period. Never again anywhere in the system does 'DC' come up. Everything is simply described as being a 'level N thing.' This is the pure distillation of what 4e was doing. If you want something to be harder, its higher level, easier, it is lower level. Circumstances don't favor you, disadvantage, circumstances do favor you, advantage. Your extra strong, OK you get an ability bonus on your check result for that roll. Very simple, very much 4e distilled to its essence.
So, when you create an adventure (frame a scene anyway) you simply populate it with things that are described as being of the level appropriate to the scene (presumably that of the PCs). Anything that is far below their level is simply wallpaper or fictionally significant in some other way besides presenting a challenge. Likewise if something was far above the PC's level in a scene, presumably there would be a special circumstance, or again it isn't directly engaged as a challenge in and of itself (IE you negotiate with the Ancient Huge Red Dragon, it is 20 levels above you, this is not a combat situation).
Right, so framing is one potential factor there. A hard check for a high level PC might be 10 hard checks for a low level PC (of his level) with bad consequences for failures, this is possible. I'd call that an 'advanced concept' that isn't something every 4e GM needs to master in order to function though. They can just set the DC as "hard for a level 20" and the level 1 guy is told "you cannot do this." Maybe he can do it, but he needs to get the blessing of Kord or something first, its not a direct obstacle he can pass on the face of it.Furthermore, in 4e the descriptors used to set a level-appropriate DC - easy, medium and hard - are used relatively, not absolutely. So something framed as easy for an epic-tier PC (say, climbing up a wind-and-snow swept mountain side to reach the portal to the Elemental Chaos at its peak) would certainly be hard for a low-level PC. It would also be reasonable at Epic to treat this as just one move in a skill challenge, whereas at heroic tier it would make more sense to frame the climb as a skill challenge in itself.
Yeah, I am a bit unsure on that one as well. AFAICT 5e seems perfectly happy to hand the same scree slope to any party of any level. Obviously higher level parties over all will handle it better, but it isn't clearly 'easier' for them, like it would be in 4e. This is where I find that 5e is much more inclined to produce a sort of 'non-fantastical' world fiction. In 4e you'd send the PCs to Tartarus to find the slope that they will be challenged by. In 5e the GM is not clearly told to do that, he can just let the action wander around in the same old locations for 20 levels. 5e seems quite equivocal about what it is actually about sometimes.This confused me a bit. The first three sentences seem to be describing 5e working as intended; but then you say "this is on me as the GM" which implies that the first three sentences are describing some sort of error or clumsiness on the GM's part. That implication is reinforced by saying "the system should be acting to save me from that choice". What's wrong with the choice?
In 4e, as I said, the presence of the scree in a higher-level situation would probably be treated as difficult terrain or a DC-adjuster. In 5e, as I also said, the wizard struggling while the fighter trivialises it seems to be working as intended.
What have I missed?