I think the acid test for anyone who says they've run high level D&D is to ask them how many times they resorted to "[spell name] doesn't work here." The most common spells probably being Teleport, Detect Thoughts or Scrying. Even CR had to resort to "teleportation doesn't work here" in the final arc so that the PC's would actually experience the cool setting rather than teleporting to the objective.
More than anything else, the problem with high levels is the number of spells that might as well read "Remove Challenge" in their description.
I'm trying to work that into the world arc I'm building.
T1 is introduction. Local heroes doing their thing stumble over something of great import (tm). I'm designing success to be optional (but I hope likely, this is T1), but
encountering it is going to happen. T1 BBEG (should it be SBEG?) is interacting with said thing of great import, and either succeeds or fails depending on PC actions.
In T1, dire wolves harassing, hillfolk raiders, kobolds guarding a shrine, and harpies pulling you down cliffs is fair game.
T2 is intended to be the repercussions of that thing of great import. The PCs have a head start on tracking down the shiny toys, which happen to be usually hidden in dungeons. Rivals crop up, also going after the shinys. I'm aiming for an Indiana Jones/Tomb raider vibe, where they follow breadcrumbs (multiple) to various locations. Finding the dungeon, interacting with the locals and the rivals, and getting the toy first.
By the end of T2, I expect them to be able to bypass most of the dungeons and grab the shiny.
T2 antagonists are said rival and rivals organizations. Some of whom I hope the PCs will learn to hate.
In T2, a dungeon ruled by an ancient mad dracolich guarding a shiny is fair game.
By T3, the once they find a dungeon, grabbing the shiny should be almost free. So two big changes happen.
First, the cold war that has been brewing goes hot and rapidly becomes a world war. The PCs will hopefully made friends with or give a naughty word about at least some NPCs or organizations, and those organizations will be involved or threatened by said war.
Second, the trail of great import + shinys point directly at an outside context problem. The war is a "kids in the playground" problem.
T3 antagonists are the warring states and their rulers, some hidden people manipulating the war and think that they can profit from it, and finally at least some antagonists who are aware of the outside context problem.
Winning or stopping the world war in T3
is a side plot.
The goal here is a bit Game of Thrones, as evidence from T1/T2 (and failing that, an NPC can simply tell the PCs) should draw a clear line that whomever wins this war is about to rule over a dead world.
In T3, a fleet of airships crewed by warforged firing volleys of earth elementals at a city the PCs are in is fair game.
T4 is about the outside context problem coming to a head. Success is not an option, mitigation is.
In T4, an entire nation being razed because the PCs took a short rest is fair game.
It's striking how often even the pros do that, all the way back to the earliest adventures (Tomb of Horrors comes to mind).
So, a lot of early modules where tournament modules, intended to be played in a short session, in competition with other parties.
That is why they where aggressively deadly and locked down options.