Good games have ONE difficulty mode. More and more red flags about this game to be honest, but I will still buy it nevertheless.
This is a rubbish statement. Armored Core 6 has 1 difficulty and is worse for it. It's a fucking cakewalk if you know what you are doing and mostly a brain dead experience.
FromSoft has always been about choosing your own difficutly ingame though.
Armored Core 6 isn't super hard by any means, but usually if you want a decent challenge, don't use Stun Needles. I mean i'm exagerating but honestly in the main that's pretty much the gist of it.
One difficulty setting is best for games where the difficulty lies in figuring out and adpating to the design. Fudging around with numbers doesn't really do much of anything in the Dark Souls games. If you can't figure out how a boss work having more health or extra damage won't help you, and trying to redesign boss patterns for the sake of having different difficutly settings would be a colossal amount of work for basically zero pay off. It's much easier, and much more logical, to give the player alternative means to overcome certain obstacles, like summons and so forth.
Difficutly settings in most games are usually half assed to begin with. Just change some numbers (damage and health values, number of enemies etc) around and call it a day. Occationally if the developers put some effort they'll maybe change how the AI work at higher settings but really that's pretty much the extend of it. This approach really does't do much for games like Souls. It's why in most of them NG+ is usually just really lame.