I can't really argue with that, but if the challenge of D&D isn't in the resource management, then where is it supposed to be?
If you're only saying that the designers weren't clear in conveying that message, then I can't really argue with that either. If you're saying that some people people might be tricked into playing D&D, because they didn't know that it's a game where the primary challenge is in managing resources, then that also makes perfect sense.
If you're saying that there's some other way to play, where resource management isn't an obstacle at all, then I'm not following you. I don't see what other obstacles the game has to put in your way.
As someone who has long disagreed with classifying D&D as a "resource management game" I find this question very thought-provoking. By focusing on the source of "the challenge in D&D" you've highlighted what may be a key distinction: I see the challenge as arising from the design of the campaign, not from the game system itself. So my reflexive answer to the question "Where is the challenge of D&D?" is "that's campaign dependent", but clearly you see it differently. If you see the source of the challenge of D&D as uniform across campaigns, it makes more sense to me that common elements of the campaigns you play--such as the source of the challenge--would be ascribed to the game system itself.
To help illustrate what I mean by the source of the challenge being campaign dependent, here are three types of campaigns I've played with wildly different sources of challenge.
First, I've definitely played in campaigns where the challenge was to overcome obstacles by skillful use of on-character-sheet resources. I recently played through Dungeon of the Mad Mage, for example, and I definitely agree that the challenge of that campaign comes from resource management via the 5e mechanics.
But I've also played in, and run, D&D campaigns where the challenge came from overcoming obstacles by skillful use of off-character-sheet resources such as such as influence, wealth (as distinct from cash), minions, and intel. These were resource management campaigns, but not as a result of anything related to the design of D&D.
Finally, I've played in, and run, D&D campaigns where the challenge came not from overcoming obstacles (that was basically a given) but from skillfully choosing which obstacles to face in the first place to best achieve the party's priorities. (Example: sure, you're powerful enough to steamroll that dragon, but would doing so advance your agenda or hinder it in comparison to whatever else you could spend your time on?) Even if a choice ends up leading to a combat difficult enough that the resource management of the combat system comes into play, that's incidental to the broader strategic challenge. In a game like this the party can successfully overcome every obstacle they face, and still not advance their goals if they chose a strategy ill-suited to the current situation. Conversely, if they can pull off a xanatos gambit they might advance their goals even if they fail to overcome any of the obstacles. The challenge in these campaigns definitely isn't originating from the game system.
Importantly, I find 5e D&D to be a fantastic system for each of these types of campaigns. As long as we're modelling the characters in the D&D system and using its core rules for action resolution when they apply, that's enough for me to qualify as "playing D&D". And since in only one of the three types of campaigns above does the challenge arise from the resource management elements in the rules, I can't agree that D&D itself is defined by those elements.
I can definitely see, however, that others might disagree with me in thinking of all three of types of campaigns I described as equally "playing D&D". A case can be made that only the first example is archetypical, and that the other two are off-label uses. From that perspective, when playing on-brand D&D, the challenge
always arises from overcoming obstacles through skillful management of the resources defined in the system because anything else wouldn't be on-brand. I can definitely see how that perspective would lead to the view that the challenge arises from the game system itself, and the conclusion that D&D is a resource management game.
So do you think the distinction between seeing the source of the challenge as arising from the campaign, rather than the game system, helps describe the differences in perspective on whether or not D&D is a resource management game? Or am I wildly overthinking this?