While I have a LOT of problems with Dark Souls 3, and a LOT of problems with its lore... frankly, none of the things you listed are problems.
Fox12 said:
For instance, the mere fact that there is a sequel at all means that one of the original endings have been invalidated. The Dark Lord ending can no longer be canon, because there was never an age of dark. To make matters worse, even the linking of the fire ending makes no sense. The whole point was that you were either continuing the age of fire, or you were ushering in an age of man. And yet, in Dark Soul's 3, the age of man comes anyway. The gods interbreed with mortals, and Gwyndolin gets eaten by Aldritch. Humanity has basically taken control of the planet, the old religions have stopped worshipping the original gods, and people have even taken over Anor Londo and fed the remaining gods to a monster. If that's the case, then what was the point of linking the fire at all? The age of man comes either way, and humanity doesn't seem to be affected by either ending. The Dark Soul, which is what the game is named after, isn't even mentioned in Dark Soul's 3.
At times DS3 feels like self parody. What was Fromsoft thinking? In terms of lore, I think DS3 is even worse then DS2. What's your opinion on the lore? Is it salvageable? Is it even worth salvaging? Or do you think the game was fine despite these flaws?
That's the entire point of Dark Souls 2. The Dark Lord ending is canon, but the age of dark still never came anyways, and Dark Souls 2 (and event to an extent Dark Souls 3 itself) shows you why. Even if YOU choose not to link the fire and welcome the age of dark, it doesn't actually matter because some other undead will come along and do what you refused to do. That's what we do in Dark Souls 2 afterall. Vendrick was the 'chosen undead', but chose not to link the fire. In essence, he chose the Dark Lord ending... and it didn't matter because we came along and did it anyways. Likewise in DS3, Lothric is refusing to link the fire, so along comes us to (theoretically) get the job done.
More than that though, even if the age of dark DID come, you also have to take into account one very important thing about Lordran/Drangleic/Lothric: All of reality collapses in on itself there. The location the Souls games takes place, as established by Solaire in DS1 and mentioned in DS2 as well, is a place where reality and even time itself is fucked up and doesn't work the way that it's supposed to. It's the entire reason phantoms exist. In Lordran, you can actually cross through the boundaries from one reality to another. And you do, and not just you, but at least half the npcs do as well. Solaire, even when he isn't actively a phantom, is not and never was from your reality. Neither is Lautrec. In fact, you see this first hand when you invade Lautrec's world to kill him in Dark Souls 1. And in 3 you are summoned into Sirris's world to help her out. Hell, you can be summoned into Anri's world to help Anri kill Aldrich... and yet Aldrich will still be there in your own world when you return, requiring you to kill him again. Because even though you meet Anri in the flesh in your world, you and him are from separate realities, each with your own version of Aldrich.
When you're told in DS3 that 'the lands of the lords converge at the base of Lothric Castle', you are literally being told that the alternate realities that each lord hails from are crashing into each other and breaking down each other's barriers, the different dimensions colliding and fusing together.
And the thing about alternate realities is that there's infinite of them. Infinite realities and infinite possibilities.
So yes, you chose the Dark Lord ending in Dark Souls 1, and that ending is absolutely canon, but just because that's the ending you chose, doesn't mean some other undead asshole didn't come along and undo your choice. And even if they DIDN'T come along and undo your work, it still doesn't matter because that only happened in ONE reality out of infinite possibilities, and so there are still uncountable worlds where that didn't happen.
A few other things to note: Ornstein appears in DS2 as well, despite being killed in 1, except having given in to the dark. It's entirely possible, even likely, that Ornstein and Smough 'survive' you murdering their asses in DS1. They could be undead themselves, cursed to return to life (with returning to life and going hollow being a common theory as to what's going on with Ornstein in DS2). Or, considering everything in Anor Londo, including even half the enemies that you fight, are just illusions created by Gwyndolin, you have to wonder if you truly killed them at all, and not just an illusion of them while they slinked away to lick their wounds.
Also keep in mind that Gwyndolin was an optional secret boss. Which means you didn't have to kill him. Which means there are plenty of realities where he didn't die. And since you are actively visiting multiple realities in DS3, it's likely that the one Aldrich ate him in was a reality where Gwyndolin survived.
And Solaire/Andre being Gwyn's son was never a thing that was confirmed. A popular fan theory, sure, with evidence to back it up in absence of evidence to conflict it, but never a thing that was proven as absolute fact.
And finally, the gods being all gone and fucked isn't something new to 3, it was like that in 1, when Gwyndolin was literally the only one left and all the others had peaced out. And that was after Gwyn linked the fire but before you ever had the chance to even make your choice whether to continue linking it or not. Because continuing the age of fire is a futile endeavour and always was, and that's the point. That said, the age of fire is in shambles, but the age of man has not yet come, because so long as the fire is linked, humans are still, well, human looking, and weak, with monsters roaming and the remnants of the gods' age pulling strings in the background. Once the age of dark begins, humanity would take on its true monstrous form, which you glimpse in the form of things like Manus in Dark Souls 1's DLC.
You ARE right that Dark Souls 3's lore IS worse than 2's, but you're wrong about why. It isn't worse because it conflicts with story events in Dark Souls 1/2, because alternate reality nonsense hand-waves all that shit away, and has been hand hand-waving it away since the very beginning. No, DS3's lore is worse than the previous games because it suddenly introduces a lot of new details to the fundamental base of the world's setting with no explanation. Like, wtf is an 'unkindled'? Why are you different/special from ordinary undead? Why are Aldrich/Yhorm/The Abyss Watchers even still alive? The final step in kindling the first flame is defeating the previous Lord of Cinder in combat, so there should never be more than one at a time, and instead we've got multiple of them. And why do we need them to kindle the first flame when we never have before? Etc. THESE are the questions you should be asking, because they're the reason why Dark Souls 3's lore is fucked up.