First of all depends whether the extra-dificulties are considered as “extra content on top” or part of it, also, depends on what “unbeatable” means, and what “masses” is considered
The problem of doing it otherwise is that you completely lock content under grind/farm/whatever, BY FAR the worst decision… Cause if that’s the case people are gonna beat the game and stop playing (and rightfully so)
Dark souls isn’t the best example, the problem with DS is “cheap death” or “instant death on first mistake” concept is used, the problem isn’t the decision, it’s the implementation. Here’s a better example (IMO): Kingdoms of Amalur - Reckoning (KoaR), now though the game was obviously not designed to be unbeatable for the masses (not anywhere near DS in that regard), it had quite of it’s own tricky moments where some “it would be best to use my super limited super power/s right now just to survive for the next round” decisions were required. Another (better than DS but not from the genre) example is Doom-Eternal, now true, it’s not a RPG, it’s an FPS (a super “on steroids” one while at it), but there is A LOT to learn/take (even if just experiment do so) from, for ex: mobs that are immune to “non-primary” AoE but if you one-shot one at a time they drop a globe (or any other type of defensive or offensive limited power consumable), or maybe Goblins that instead of loot drop consumables necessary to survive down further… Really, it comes down to implementation, we’ve been far enough in the “focus” to know what works and what doesn’t, and I tend to think that “play a demo to win the game then grind or farm for progress” simply doesn’t do the justice of time and gameplay investment tbh
Also, the last part of your reply means nothing and is very bad/shallow and doesn’t mean nothing on it’s own… Not because “Hack & slash ARPG” isn’t a thing (or is it ?), but rather because it’s a label, and quite frankly likely a useless one while at it
Would advice to not categorization by label/s, but think each “feature/mechanic” of their own, if Blizz thought that way “hack & slash RPG has X but not Y” then they wouldn’t even have came up with a class-specific feature or trigger-effect runes for example… (or even a 2nd “resource” for the DH back in the days of D3 opener)
It’s recommendable to not “limit” functionality based on label (in fact it’s super bad mindset that hardly has any merit at all), for the sake of achieving the goal of making the best of most worlds possible 