Rogue-likes and "What is hard?"
I think the question is missing the point. It's not about "difficulty." It's about
playstyle. Permadeath is a valid game mechanic, and it is appropriate in certain venues. I don't see anyone suggesting that chess would be "better" or "easier" if your king respawned, requiring that he be captured three times before winning.
That said, it can be a disconcerting mechanic for people who are unaccustomed to it.
A significant part of the experience of a game is the emotional affect it has on us. There is a certain thrill to be had when downing a raid boss, when recovering the amulet of yendor, when mining adamantine. It can feel "good" when we feel like we win. But to some extent we measure the significance of feeling by the amount of change a thing evokes in us. The joy of having a chocolate bar might be less if we have a chocolate bar every day.
As such, there are two different models of that "Feel good" at work here. If you feel "ok...ok...nothing great...ok...WOW THAT'S AWESOME!" that represents a scertain sort of change of emotional state. And it's a valid change, and one that people can enjoy. On the other hand if you feel "ok...ok...DAMN THAT'S AWFUL...ok...ok...WOW THAT'S AWESOME!!!" that represents a different sort of change of emotional state. And it is also a valid change.
Permadeath games offers a wider range of emotional states: both very good, and very bad. No-permadeath games range from ok/bored to very good. It's a smaller range. But, one with teh benefit of never needing to feel very bad.
Both are valid.
Play games that you will enjoy.
overly hard for "hardcore" gamers
Again, this is missing the point. I wouldn't say that Angband with permadeath is necessarily more difficult than a WoW raid boss in which you can ressurect infinitely many times. However, games with permadeath
play differently.
For example, one can easily create a backup savefile for most roguelikes, and play that way. Any time you die, restore freom backup and POOF you've just been ressurected. But I challenge you to play a game with permadeath this way, and then play without it. Much changes other than merely the ressurection. The
way you play will also very likely be different.
Using Angband as an example, backing up savefiles it becomes practical to avoid carrying teleport and phase door scrolls, you can avoid carrying potions of cure critical wounds, and you can delve much more deeply more quickly. It becomes practical to delve deep hoping for a lucky drop. If you coem up short a mandatory resist, you can keep descening anyway, because there odds aren't all that high that you'll need it. And if you die, just restore.
But you'll notice that by playing with backup savefiles, many of these things that you don't need...are game mechanics that you're
not playing with. You can beat Angband without using backups, but doing so it becomes important to use those scrolls and potions. It becomes important to gear your character correctly and completely. It becomes important to be patient and only tackling what you safely can rather than charging blithely ever onward scumming for lucky drops.
It becomes a different game.
Both are valid.
Again, play games that you'll enjoy.