Let's reduce it further and say they're nothing new or impressive because we're still just using controllers and keyboards to hit buttons and make the things on the screen do things.
I would argue that FROM games are both ambiguous AND feats of master-crafted world-building. I think achieving a level of engagement with players that finds them exploring, discovering, discussing and speculating with each other years after release is an impressive accomplishment. Most games I've played I was content to complete once, and the vast majority of those, I had nothing to say or consider once I was done, i.e.: I saved the princess, saved the world, slayed the dragon, and my experience was identical to that of likely everyone who played those same games. Did I enjoy them? Sure. Were they remarkable in the literal sense of the word? Mostly No.
I mean, if I laid out my chronology of DS3, I'd be impressed if you found anything signfiicantly different in yours (other then we maybe swapped order on killing the Giant and the Twin bois. DS2 of course had its very Zelda-inspired 4 bosses to open the castle thing but within that context not a lot varied. DS1 I forget which things you could specifically swap but would generally fall into the same mold.
I killed the four great souls/lord souls/lords of cinder/demigods and went to the designated out of time and space Nexus point to fight the last/first person that did this tirck and they turned into a somewhat more abstract person to fight and then we rebooted the world. If I remember to talk to the right people 12 times at the correct intervals then I get to choose the other option for a different cutscene in which we reboot the world.
Is there a variance? To some degree, any sizable game for instance has side quests generally, particularly in the RPG space. Very few (or probably none) that have a story will allow much true deviation. OH, you'll get alternate endings or your good/evil path but the game will playthrough the same at the end of the day. New Vegas has the same overall variation in the story as Mass Effect 3, just presented infinitely better and not albatrossed by a decade of hyping how it would be different.
The discussions you mention are hardly unqiue or even rare to Souls. Warframe has its share of lore folks, so does Monster Hunter (which is almost impressive how far they stretch two words on the description of a pair of pants), so does Deep Rock Galactic, No MAns Sky, Destiny. Almost every game that isn't essentially a would-be movie with some gameplay segments (A la the Last of Us, and I wouldn't be surprised if theres still some would be lore videos out there trying write fanfiction of random audiologs or whatnot)
I wouldn't say that Dark Souls is unclear on "what" is going on either. The chosen Hollow/Ashen/Tarnished kills all the demigods and relights the flame/rebuilds the rune/etc. Its staggeringly simple and the reason people think its vague is that its staggeringly simple when they're used to plots about 3000 year old conspiracies and love interests and politics. Which Souls has no time for. It was in its early, hype, often cited for being a back to basics approach owing more to NES or SNES games where the story was there to move you along, not for us to wonder what grand motiviation the Belmonts had for hunting Dracula or the like. Maybe you are an actual chosen one, or maybe they nicked the subversion from Morrowind (in itself nicked from Ultima) where the chosen one is whoever fulfills the prophecy and there is no rhyme to it other then "First person who tries and succeeds)
The only real vaguery of any import in them is what one interprets the Flame/Elden Ring to actually represent. As noted above (and semi-consistent across a lot of JRPGs) it mostly seems to be an abstractionism of by and large, tradition as a concept. In a fantasy RPG, that typically manifests as religion, as that sort of thing was dominant in those eras. Dark Souls settles with exiles/outcasts doing the job rather then a motley crew of neon-haired teenagers with too many belts, and (thankfully) eschews a lot of the nonsensical self-regurgitating writing that usually weighs other JRPGs down but sticks prettymuch on the same path. The fanbase for whatever reason feels compelled to try and add a bunch of nonsensical self-regurgitating writing to it, which in itself wouldn't be a problem if people didn't keep posting these fanfiction-adjacent things into any actual discussion of the games story.
Mechanically in a "gameplay" progression and layout, and order of things its prettymuch just straight cribbed off Zelda, by the creators own admission. Most evident in Dark Souls 1 which literally clones "get the things to unlock the not-actually final area which then unlocks then the second set of real dungeons" structure of Link to the Past and Ocarina. Which is fine, its a structure that works (which is why Nintendo used it for like 35 years)