It's funny you mention Uncharted since Uncharted 2 is widely considered an influential game and Uncharted 1 isn't.
Uncharted 1 was PS3 game of the year at IGN, at least. It was one of the first significant games for that system. Uncharted 2 is a great game, but it doesn't innovate over Uncharted 2, it only refines the formula that Uncharted 1 invented. Saying "no one thinks uncharted 1 is influential" is flat out false. Uncharted 2 is by far the better game, but only because Naughty Dog was able to create the formula for success with Drake's Fortune.
Without the built in audience from UC1 being a hit, UC2 doesn't have the budget and doesn't have the sales to make it a smash hit. Uncharted 2 can't happen in a vacuum without UC1 preceding it, just as Dark Souls' success can't happen without Demon's Souls being developed first.
Spending "soul points" to upgrade your player? Starting classes that evolve over time into specialists OR jack of all trades? huge weapon gallery upgradable by elemental stones? Giant, screen filling crazy hard bosses? Invasions by other players? Players BEING a stage boss? Bloodstain retrieval of unused exp? Player phantoms telegraphing death? Messages left by other players? Hostile NPC's murdering other NPCs if you don't stop them? Hidden player NPC Quests? The entire quasi-medieval theme? Started with Demon's. That's where the formula comes from. Remove these things and you don't have a souls game at all.
Do you think Namco/Badai picks up Dark Souls as a high budget multiplatform title without Demon's Souls becoming a sleeper hit no one saw coming? spoiler alert: No.
But with the FF6 vs 7 comparison, yeah the tech is different, but FF6 had a huge cinematic focus which FF7 continued.
The difference here is that it's not just something vague like "cinematic focus" (and FF4 would be where that started, really, not 6), it's literally EVERYTHING about Dark Souls is something that Demon's innovated first.
As far as sales go, I'm not seeing any reputable sales data for Demon's Souls. The 1.7 million is just an estimate by a Forbes article many years after the game came out with no indication of what they used to base that on.
I linked an article with some sales numbers earlier in the thread that don't come from Forbes- but again no idea how reputable that is. The best way to determine how successful the game is though is how well it does on similar platforms. Otherwise you're arguing reach of the game, not the overall appeal. In terms of how well the console versions of Demon's and Dark did, every shred of information we have says the two were very close. within a half million to a million units.
As far as gameplay goes, Dark Souls made a number of changes which led to it achieving more widespread success, including the interconnected map, more emphasis on online, big improvements in resource management (flask system, no inventory limit, magic uses vs MP), and covenants.
This isn't true at all- the interconnected world is a difference between the two, but Dark Souls didn't invent that- that's an innovation that goes back metroidvanias- and the interconnected world aspect completely ceases once you hit anor londo and no longer applies- after that the game is a series of dead ends that have to be teleported out of or backtracked.
There isn't "more emphasis on online." Demon's has a DEEPER online integration than dark does! Invasions were invented for that game, but so was world tendency (which Dark doesn't have). Unlike character tendency, World Tendency was inextricably linked to how the online community was doing in a particular world- moving it darker or lighter over time. Since there was one dedicated server for that game, Demons souls routinely did "pure black" or "pure white" events that would perma-shift everyone's world into an extreme state in which completely unique monsters, items, and phantoms would appear.
The Dark Souls Covenants are completely half assed in comparison- and half of them were flat out broken and didn't work as intended.
The resource management thing is different, but not necessarily an improvement. Flask vs. Grass, Inventory limit vs. no inventory limit is personal preference. And as for magic uses vs. MP- Dark Souls 3 went back to MP over Magic "Charges"- exactly as Demon's did in the first place.