I'm a little confused.
How does campaign pacing impact world building?
Let's turn it around. Campaign-building, which subsumes world-building, establishes an appropriate range of campaign-pacings. If the game is balanced around a certain number of encounters between rests, it encroaches on the DMs prerogative to establish whatever the heck pacing he wants, or to put it another way, narrows his choice of campaigns he can run, without modifying something in that balance equation.
He could change the pacing and tone of his campaign, making it more frenetic and consistently working in time pressure. He could change the rest-duration/frequency factor and run his campaign in a languid years-and-continents-spanning sweep, instead. He can re-balance classes & monsters to free up a varied range of pacing options without changing the rest/recovery rules, and run a varied range, with some adventures frenetic and against the clock, and others of more sweeping scope. Or, he could accomplish similar results by ruling on the opportunity, timing, duration, and benefits of rests differently depending upon the pacing he's currently using.
There are clearly many solutions, but most come down either to fitting the campaign to the mechanics (whether that's the default mechanics or a module) or re-building the mechanics (whether that's the classes/monsters or the rest/recover rules) to fit the campaign.
The former sort place less demand on game-design skills, but create restrictions on how you run your campaign.
I acknowledge that creating a fully realised, perfectly consistent world cannot be done based on RPG mechanics. I disagree that we cannot reflect on those mechanics and incorporate them meaningfully into our game worlds.
In that context, 'fully realized' and 'perfectly consistent' are in tension. You can have, or strive for, a perfectly consistent world based on consistently applying perfectly clear & consistent mechanics (or with 5e-style mechanics, recording every ruling and treating it as iron-clad precedent) without regard to, well, anything else. At best, you may end up with a Pratchett-esque world, but that could be entertaining.
By the same token, you could come up with a fully-realized world without any mechanics - or game, or players - great authors do it all the time.
I am still trying to understand why this is a given though (well outside of personal preference)... why should or do the encounters for PC's have to apply to the populace at large? I've seen no real explanation for why this must be true... well again except for personal preference
It's the difference between approaching the world as nothing more than a painted back-drop for the PCs adventures (an absolute 'narrativist' approach), and approaching it as a 'real' place with an objective existence & set of laws in which the status of 'PC' has no meaning or impact (an absolute 'simulationist' approach). Those are two extremes that probably aren't really applicable to any actual game anyone were going to run for more than a session or two (before their players all mysteriously get too busy to show up), but, in theoretical discussions like this, they come up, because extremes are easier to construct models around.
and at that point it kind of proves this isn't an objective thing but instead something a particular DM chooses to make true in his world and thus chooses to create the associated problems around it.
One thing that DM Empowerment definitely does is allow us to decide how our we & our players will experience the problems caused by problematic aspects of the system.
We can take the default system, and run just let the campaign play out organically, and just deal with encounters generally being 'easier' than they say on the tin, and classes being decidedly imbalanced, and just let it sort itself out - players will naturally gravitate towards the most effective class they can enjoy playing, and DMs learn how challenging encounter really are.
We can take the same system and impose a story-line that consistently applies time-pressure and other factors to make days where 'the action' happens fit the encounter:difficult:short-rest:long-rest ratio that theoretically helps with avoiding the above.
We can make (possibly very extensive) mechanical changes to the game to allow it to run in a balanced/consistent manner without either of the above being considerations.
But, no matter what we do, some price is being paid.
That's the 'objective' portion. The 'subjective' portion, is that some folks may be downright enthusiastic about 'paying' a certain 'price.' The group who all want to play long-rest-recharge classes and revel in overwhelming trans-deadly encounters with nova tactics to turn them into cakewalks, for instance, will not consider the first option a 'problem,' at all, they'll consider it 'supporting their style.' Heck, they might still keep playing 3.x/PF because 5e doesn't do a good enough job of providing that support.
Whether you have 20 1/8th cultists, or 8 1/2 cultists, those farmers being sacrificed aren't going to be able to resist. In a deadly world like that, farming dies unless moved withing city walls or a standing army patrols constantly.
UNLESS the world is just a backdrop for the PC's extraordinary adventures. Cultists appear an wreak havoc only when such has a role to play in the heroes' story arc. For centuries before, no one may have heard a peep from this cult it's just an old mostly-forgotten tale, the it just happens to spring up in a deadly resurgence just as a band of heroes just happen to band together who are able to stop them.
Because: fiction.
