I think what the assumption actually is is that there is such a thing as a fixed skill DC or saving throw.
Which there is - it's written in numerous monster statblocks such as the Gelatinous Cube (CR2 DC12 Strength to escape) or the Glabrezu (CR9 escape from grapple DC 15) or the Froghemoth (CR 10 escape from grapple DC 16).
I didn't realise the switch from skills (most of which don't level up for most people) to saves (most of which don't level up for most people) when both get harder on the same schedule would be seen as some sort of goalpost shifting. It wasn't intended as such, just the first examples that come to mind. And when we use only the area of the goal that you think is appropriate the answer is still the same - there are actual hard coded DCs in 5e (just as in any other edition) and if the PCs don't level up they fall further and further behind and get less and less able to be competent against equivalent threats.
Where did this come from?
My argument is threefold:
- Skill DCs have meanings that are hard-coded into the game. This applies in 4e and in 5e - as demonstrated by grapple checks.
- Related to this if it's a DC 15 check to leap between rooftops in one adventure the players will be surprised when you make it DC 10 to leap between the same two rooftops in a later one. Consistency helps
- Characters generally in my experience like to have a base of operations rather than bouncing from adventure to adventure with no home. So you may well reuse environments.
But being able to reuse the low level bad guys in large numbers is part of the
point of Bounded Accuracy. Levelling up from fighting for your lives against a few orc scouts to taking on a small orc army lead by a dark paladin with warlock support is a perfectly decent adventure chain. In 4e you're eventually going to turn the orcs into minions of course.
Easier. +2 for something to grab on to.
No necessary practice avoiding being swallowed - but plenty of physical activity. Are you genuinely and sincerely telling me that a pasty bookworm who's barely been out of the library is going to be every bit as good as wrestling and wriggling out of things as a hardened adventurer used to rough sleeping, who's been in physical fights, and forced by their party to take exercise?
Yes, of course a gelatinous cube is just as dangerous to a level 1 wizard as a level 20 archmage in 5e. Riiiiight.
A purple worm has static DCs in both 4e and 5e.
The difference is that in 5e if you aren't explicitly competent at something you're incompetent at it. In 4e it's assumed that as you adventure you get better at things like knowing what signs to spot, you get fitter physically, and more knowledgeable about the world in general because you've been more places, seen more, done more, and pushed yourself harder.
In 5e the wizard taking excercise doesn't make them any fitter. The fighter picks up nothing from the campfire arguments between the wizard and the cleric. You are assumed to effectively be in a bubble as you only level up what you specialise in, being blind and incurious as to everything else.
Nope. The worm is not "hard" whenever you encounter it. It's
DC 19. In 4e it's
DC 21. In neither case do they use the Easy/Medium/Hard scaling - in both cases it's a static property of the worm. The only difference is that in 4e characters are expected to get more physically competent as they level up, do more, and see more. In 5e the pasty faced nerd of a wizard never gets a tan or any muscle tone and the barbarian never learns anything from watching the wizard work.
And a character that doesn't put build choices into improving that save might as well never have left the library for all they've learned. This is the problem. Now there's a strong argument that the scaling in 4e is
too strong and should be a point every four levels rather than every two. But if you've been grappled by zombies, had to run out of a collapsing castle, hiked dozens of miles a day, and other things then escaping from a purple worm is going to be more like things you've done than if you're a scribe who never leaves the library.