Dark Souls is not an RPG. Not anymore than x-com is, and that is not to make fun of the idea; x-com has a bit of RPG in it! But before we go down this route, let me begin by briefly discussing everyone's favourite question: what is an RPG?
I have commented on this question before. In fact, I guess if you get down to it, I joined the Codex because of this question. This is the only place I ever found that tried to tackle it with any amount of effort except by the forge. I have myself changed opinions on this sometimes, but here is how I see things: An RPG, when we consider the tabletop activity, is defined by the interaction of the people playing around the table. It is, specifically a kind of both game and storytelling, both at the same time. People compete to complete objectives while at the same time listening and telling a story (for a sufficiently loose meaning of story).
This double nature creates in RPGs three aspects of play, which I think are somewhat well explained by the narrative agendas the old Forge used to go on about. The gamist agenda is correctly associated with the game in "role playing game". Whether it is the straightforward mastery of combat, the mastery of character building, the creative use of your tools to solve problems, the manipulation of NPCs or PCs into doing your secret objectives or even simply seeing who comes up with the most interesting character or who has the most amusing roleplaying... The point is that while we are talking about a game here, this is a game in the meaning of being a contest, challenge or competition, not of being a formal mathematical system where "players" can take predetermined actions with mathematically well defined results. The other two agendas are concerned with the story, and I think it may have been a mistake to separate them explicitly. Basically, the simulationist is concerned with how the game world is presented and that its internal logic is followed and well presented. In a way, it concerns itself with how the story is read. Creativism on the other hand is concerned with what the story is about, themes, story arcs and such. The main difference here is, as far as I can tell, that creativists were annoyed by games that had rules describing the imaginary world and rather wanted meta-rules that thought in terms of what the story wants to tell the players instead.
In the end, I think the forge erred by thinking those things were really separate or that they formed independent agendas, when they are really present in any game. But they did do well by trying to understand these three modes which have profound impacts on the game itself. But enough about pencil andhe paper games and onwards to CRPGs.
The thing about a CRPG is that it isn't, if I am correct, a real computer game genre. Not anymore than "fantasy" is a game genre. Game genres are defined by a specific type of gameplay, that is, how the game engages and challenges the player. A game like Super Mario, for instance, engages the player in a challenge of reflexes and precision. Specifically, given how the player views the world and how many of these challenges are about jumping, it could be called a "platformer". A game like x-com, on the other hand, engages the player by having several rules mimicking a real world confrontation (such as having a per unit line of sight based on a 3d world (even if the graphics are 2d) that is affected by lighting and smoke from smoke grenades) inside small skirmishes and a long term planning game all rolled in one package.
The point of these games is in this gameplay, in how they engage the player, in what kind of skills they test and help the player build so he can progress in the game. However, there is no specific gameplay to RPGs. These are instead defined by secondary characteristics. Context, options when creating a character, options on how to interact with NPCs (and frequently these interactions have nothing to do with the game itself anyway) are things that will help shape a computer game in a CRPG. As for the gameplay... it could be anything! I don't mean to say here that gameplay doesn't matter to making a CRPG, but rather that any kind of gameplay could theoretically be used to make one. An action game, an FPS, a stealth game, an adventure game, a strategy game and even a rogue-like could be used to make a CRPG. In fact, most of these games will have elements of CRPGs, since computer games are rarelly completely abstract, and as long as your game has some non abstract elements, it has a gameworld behind it and thus some elements of an RPG*.
The point here is that there is no such a thing as a "pure" CRPG. What we can find are games that take after the P&P game more or less well. A computer game can't be storytelling, at least a single player one (I will leave MMOs and games like Space Station 13 out of this conversation because they are a whole different category). Instead, it can have elements of interactive storytelling, and those can even be connected to gameplay. But they can't be gameplay itself, which must first exist already from another genre. In P&P games, on the other hand, the gameplay and the story are supposed to build off each other. So, in D&D, while you might have a specific number of hit points and spells and damage for weapons and chance to hit, you can also plan considering the specific story and setting of the game. If you have a magic item that grows into a house, you could try to kill a dragon by getting it to swallow it and activating it, and doing so also creates part of the story of the game. On a computer game, however, this option will only be present if it was thought beforehand by the designer and the gameplay has to be shaped to accommodate the action.
Still, not all gameplay is equal. In the old days, there were debates here in the Codex about how reflex based gameplay got in the way of playing your character by making your attacks based on player skill rather than character. I think this isn't a great complaint, after all, if there wasn't some player skill involved, it would be a simulation. But it is not a completely misguided idea. Having the resulting gameplay of using such skills be more or less dependent on your character sheet makes the game approach an RPG better or not. For instance, in Fallout New Vegas you can still make do very well with a character who is a crap shooter in theory, by simply using well your weapons. The problem here isn't that a good player can conpensate for a bad character, but rather that the character skills has lower impact to the gameplay. Whereas a system where hit chance is determined by character skill only doesn't have to worry about this specific problem.
Now, with all this out of the way, I want to consider Dark Souls II. I won't consider other games because I have not played them, but I assume they are similar. DS2 actually does some things very well! For instance, the difficult gameplay meshes well with the way the character system works by having players with different character, that is, with different attributes and equipment set ups, play very differently! This is a very good thing for making your game more RPG like, and it is certainly something anyone could try to look up to and copy.
But the issue is that while this helps, DS2 focuses way too much on its challenge, on learning from mistakes and its action gameplay, to do as good a job as an RPG. The issue here isn't the game being too hard, or even too actiony, but rather that most of the game is spent with those things with little effort put to give a narrative significance to what is going on. Dying, losing your human form and then recovering is a cool idea, but it impacts little in the context of the imaginary game world. Choosing to be a hexer doesn't change much about how your story plays out except by how you attack your enemies. Entering the worlds of other players is actually a very fun mechanic, but killing the same boss four or five times doing that makes the story seem to have little sense.
Compare this with Bloodlines from Troika. Bloodlines suffers from a much more stillted and even broken gameplay. The game has several faults, and you could argue that DS2 actually incorporates your choices about your character much better with gameplay than Bloodlines. But for all of these faults, the gameplay, exploration and narrative of Bloodlines is more connected with your PC, with how you made and make him, both in character sheet and in the relationships he has with other NPCs, than DS2 does. DS2 is worried first about being a good action game and any RPG considerations are secondary.
Thus, I think it is correct to say it isn't an RPG, not because it has no elements of that; in fact I think it does better than many JRPGs, but because the concerns with role playing are still secondary compared to a full blown CRPG.
*To be exact here, it has an element of story gaming, that is, games that combine with story like an RPG does. However, not all of them are role playing games because the later also involve associating with players some specific roles. However, since this is incidental to the topic, I will treat the terms as interchangeable.