The players are stupid if they deliberately take on a challenge they cannot possibly defeat nor escape from if they engage it (hello obvious my old friend!). Every edition of D&D provides many of these lopsided match ups.).
Eh, so you say... but if you are clever enough there are ways to defeat the supposedly "undefeatable". Can't a dragon drown, suffocate, be buried alive, tricked etc.? I also noticed now you've added "or escape from..." that's a pretty big conditional there, and I don't think most PC's walk into even what they think are easy or moderate challenges without some way out.
This doesn't alter the fact that the rules dictate some challenges are insurmountable to the players if they're not high enough in level, and that at any given time during the campaign a good DM has to populate the environment with surmountable challenges, in addition to providing ample information/hints as to which ones are not..).
Insurmountable if they charge in guns a blazin or plain insurmountable no matter what they do? You know defeating a challenge =/= killing it...right?
Also no one has said you shouldn't populate the campaign with "direct combat" surmountable challenges. If you used all "direct combat" insurrmountable challenges it would be just as lopsided and unnatural as using only "direct combat" challenges that are always surrmountable.
Which means the DM is actively taking steps to ensure level-appropriate challenges exist.
Yeah, he is, but I love the way you are trying to twist this... I repeat...
No one said there shouldn't be any level-appropriate challenges... what we are ascerting is that there shouldn't only be level appropriate challenges for certain (sandbox) types of games otherwise you are limiting and restricting the choices (and possibly the creativity) of your players.
If you say so...
I didn't say they were the same, one method affords more player choice. Both have the same goal: make sure level-appropriate challenges exist for the players to take on. Both methods contrive the world into a place the game can take place.
No, they don't have the same goal and that's where you're not understanding. The I only create level appropriate combat challenges DM has that goal... in fact with this method it's the only possible goal he could have. And the player doesn't have a choice plain and simple the DM accomplishes this goal no matter what...
The DM who uses level appropriate as well as non-level appropriate combat challenges can actually have various goals such as... you decide your own fate, destiny, risk and reward... and it is accomplished because the PC's actually have to choose.
Both also restrict the number of level-inappropriate challenges the players face, one directly through outright control of the encounters themselves, and the other indirectly through reliable information and use of 'invisible walls (ie, the CR 18 dragon on Mt. Fang that hunts in the Forest of Perishables never decides to torch the village of Starting Hamlet, at least while the low-level PC's are there shopping for 10' poles and flaming oil).
Wrong, one eliminates the number of level-inappropriate challenges the players face...the other, depending on how the world is constructed could possibly create the result of restricting the number of level-inappropriate challenges the players face... or it may not. As an example what if I just have a wandering monster chart based entirely on environment as opposed to based on level, how does this in anyway restrict level-innappropriate challenges?
You assume alot and you really shouldn't. If I roll the CR 18 dragon on the wandering monster table in the village of Starting Hamlet... then the PC's will deal with it. Of course since the villagers are scared, giving the dragon tribute and doing whatever it wants, I gotta ask... why would it attack an insignificant village and destroy everything it's getting from the villagers?
(logically there's probably like a 1% chance of this happening unless something major changes the situation... would be the reason it isn't likely happening in my campaign...YMMV of course).