In both cases, because if those I-never-want-to-lose players ultimately get their way this game is as dead as a dodo.
How does "high-flung action, bold decisions and resources that refresh quickly." equal "I never want to lose"?
Heck, when you were playing DnD and you were skulking around avoiding fights, killing goblins with smoke poured into a cave, and dying if you were bit by a centipede, did you WANT to lose? Did you sit down with your 1e character and say "Alright, I'm so excited to lose against this dungeon!"? Of course not. You wanted to defeat the dungeon, that is WHY you skulked around, avoided fights, and all that other stuff. That is why the hirelings used 10 ft poles to check for traps.
The difference here isn't that one playstlye never wants to lose and the other playstyle accepts loss. The difference is the presentation between "Saving Private Ryan" and "Captain America: Winter Soldier". Both sides don't want to lose, but one side is telling a story that involves a lot of high-action and dramatic fights. One style is "avoid fighting at all costs, because you might die of an infected wound" and the other is "Drive them before you and cleanse the land of evil".
That doesn't make one better than the other, they just fulfill different story goals. And frankly, saying that the game would be dead for making it more about high-action seems to very much underestimate what people WANT from a fantasy game like this.
Where I posit, yes it should - it should be challenging for everyone regardless of experience*. And if some of that experience comes via the school of hard knocks, I've no issue with that.
* - hell, if chess can manage it, why can't D&D?
Chess is an interesting example to bring up. Do you imagine that chess puzzles are equally difficult for both new and experienced players? I don't. I imagine a Grandmaster of Chess can trivially solve most chess puzzles except those specifically designed to challenge grandmasters.
Meanwhile, there is a far more interesting comparison here with Chess. Does a Grandmaster find equal difficulty in defeating a High School Chess Club member as they would another Grandmaster? Again, obviously not. What makes Chess equally difficult regardless of experience is THE OPPONENT.
And who are the player's opponent in this scenario? It has to be the DM. The DM is the only intelligence moving the pieces on the board other than the players. So, if you want DnD to be like Chess... it is. It falls to the DM to make the scenario challenging, because the pieces that the newbs struggle to remember how they move are the same pieces for the Grandmasters, who find no challenge in basic strategies that make the newer player's heads spin.
OK, design mistake right there. If the game's to be built around combat (which, three-pillar ideals or not, it still is) then combat ought to provide the primary challenge...or, put another way, the easiest access to loss conditions.
You are misunderstanding. Combat is the easiest way to access the loss condition. It is actually about the only way to do it. However, the challenge of the game for experts isn't found in the statblocks. The challenge isn't found in a rule that says you take double damage from every hit.
The challenge of the game, from the player perspective, comes from the Dungeon Master's arrangement of the pieces. A horde of 10 zombies isn't a challenge for a level 5 party. A horde of 10 zombies hidden in a poison cloud might be. A horde of 10 zombies hidden in a poison cloud where a quest item is also hidden, meaning the players need to fight and search at the same time, and the area is a maze of tunnels could be insanely challenging for that party.
But the zombie statblock doesn't tell you to put them in a maze filled with poison gas. It can't tell you that, because they need to be used in many different ways. And the tools to design that encounter are all in the books. It's all there. You just have to piece them together.
All good ideas.
My point is the DM shouldn't have to do this as a homebrew, it should be baked in as a variable. Example, in the monster write-up it should say: "Gnolls are always armed with at least one dagger plus another weapon: 40% carry 1d6 spears, 20% carry a longsword, 20% a glaive, 15% a morning star, and 5% an exotic weapon of your choice."
No. I don't need it to be 40% or 20% or anything like that. If I want them to be equipped with different weapons, then I equip them differently. And the books spell this out. The MM mentions altering monsters on pg 6 as a sidebar, talks about equipment changes on pgs 9 and 11. It is all there. They told you exactly how to modify the enemies. What they didn't do was write a variant for every possible type.
And frankly, thank the gods they didn't, because the MM would have tripled in size. Sure, this is "technically" homebrewing, but it is also just pure modularity of design. You have the tools, put them together how you want. The statblocks are just the base templates.
For me it's the other way, at least when it comes to player pushback: it's stupendously easier to tone it down than it is to ramp it up.
I'm considering some rules tweaks in the near future, with roughly a net no-gain/loss in overall character power; and I already know which ones will be met with gleeful acceptance and which will garner the complaints.
I don't care about player pushback. I care about the ease of actually doing the thing. I've just listed a ton of ways to make things more difficult, but it is a lot harder to know how to make it easier. Honestly, like I said, it is additionally very hard to know if you CAN make it easier when you are first starting out.
Indeed, but we all got that experience somehow and I'm willing to bet most of it came from editions far more challening than this one.
Sure, and ancient people learned to hunt because they starved if they didn't. Doesn't make it BETTER to learn hunting under those conditions.
Just because older editions were more challenging out of the book doesn't mean they were better, or that people enjoyed them more. I've had many people either quit or almost quit DnD on me because of how hard it was for them to make a 5e Character. And you may scoff, because 3.X characters were so much more complicated. But do you know what that really means? That means that those people who might be interested in the hobby as a way to express their creativity would never play. They'd see how hard it was and say "Ah, this game clearly isn't intended for me" and leave.
You are a DM with decades more experience than myself. If I can figure out how to alter the baseline of 5e to be challenging, even as I buff player abilities, then I'm certain you are capable. But for those people who still don't understand even the simplest parts of optimization, I'm glad the baseline game is a bit easier. Let them learn and grow, and then SHOW THEM how to ramp it up when they are ready, rather than complaining that all new players only care about winning and will destroy the game.