I think part of the problem is D&D's resource management is locked to "dungeon" style of play. The PCs are far away from home, in hostile territory, facing multiple hostile encounters in a short period. Resource management breaks down when the PCs aren't in hostile territory (such as urban adventures), have access to renewable supplies (like shops and inns), and aren't supposed to face multiple encounters but instead a few larger set piece adventures. Tack on variable time pressure (to allow for short/long rests) and PCs face every encounter with nova potential and limited risk.
For me, the question was never one of dropping my players in Undermountain and seeing if they can manage resources. The issue comes when I put them in Waterdeep and they can face every group of thugs, treacherous nobles, or murderous cult with full power and then easily use the resources of the city to heal and restock. That's where D&D resource management fails.
Isn't Waterdeep (or any big city) not another maze? And if they kicked the hornets nest, wouldn't getting to other locations not also provide hurdles when the enemy also knows the city well or better then the party? Facing another group of thugs suddenly becomes a LOT more dangerous when they alpha-striked the first group and the next group is between them and their supplier of healing potions... I think it's about
educating players in a different play style, for if you let this happen continuously without consequence, nothing will ever change and no matter how you redesign it, they will continue to behave this way.
And it's not all that strange if you think about it. If I go out biking, I can go full speed when I know I don't have anything important after biking, I can get home sweaty and tired, ready for some rest and relaxation. But if I know I have work, or a dinner, I'm not going to go nuts biking. When the players know that after encounter #1 they can go home for some rest and relaxation, they'll go all out on the first encounter. If they are not so sure or know they can't, they might be more frugal with their resources.
And if they're resting their long rest, they can get assaulted by even more thugs or even hired assassins...
To be honest, it's not that the system 'fails' outside of the dungeon, it's the DM that fails. You either do one encounter by design in an urban, woodland, etc. setting or you do multiple, and each choice is on the DM. And if you only do one encounter, that's not a problem imho, due to the alpha-strike nature of the characters, they can handle a pretty big encounter, just be sure you know what that is exactly before you start throwing heavy artillery in their direction. But you don't
have too stick with only one encounter outside of the dungeon...
Think of it as an action movie: In this scene the heroes just used all their ammo and handgrenades to take out the gangmember hideout, but they called for reinforcements, which show up and chase the heroes.