And how are you defining "diminished quality of lore"?
I wouldn't say that detail is the same as depth in terms of lore and narrative. For instance, the whole superstition that all Durin's are all essentially the same person isn't really depth. It doesn't really add anything on its own, and since Tolkien never really confirmed the truth of the superstition within the narrative he never explored the implications of it. It's just detail. So ignoring that detail in the show in order to add more dramatic depth via character interaction isn't really a diminishing. The same can be said for a lot of the changes that I have seen complaints about.
It doesn't really need benefit of the doubt because it's an adaptation nonetheless. You also just described how it added MORE depth to a character that was lacking in that department in much of a source material. We're talking about characters and events that Tolkien never really fleshed out to begin with, so the idea that what this adaptation is diminishing the depth of the lore is kind of silly.
These changes also don't do anything TO the book canon. It remains in its original form one way or another. And (if you consider the show connected to the PJ movies, as they obviously share much the same aesthetic choices) there hasn't really been anything so far that results in drastic internal contradictions. Show Galadriel can still very much follow a path that gets her to the point of Cate Blanchett Galadriel.
Well, the term "bastard" very much carries with it derogatory baggage, even if on a basic level it's simply describing a child born out of wedlock. It doesn't really seem like a good word to use if you want to convey a neutral position. If you're using the term to suggest a work that has been corrupted or diminished then you're more than likely using subjective determinations of quality to compare the adaptation to the original.
That kind of sounds like the opposite of what RoP is doing by fleshing out characters, giving them arcs and agency, and more interactions with each other.
But you haven't explained WHY!
Regarding Durin, you mentioned two points of confusion that specifically have to do with knowing lore that is outside the scope of the show and has no impact on the narrative. So other than detail for the sake of detail, what is the issue? Where is the train wreck?
You understand the goal of the show, to portray the events outlined in the appendices on the screen as part of a connected narrative. These are events that Tolkien essentially jotted down with a list of dates and very little depth whatsoever. Very little detail is given, most of the characters have no written dialogue, there's almost no narrative or thematic depth to any of it. If the adaptation can bring these events together with a handful of characters over the course of a protracted timeline, AND it reaches the appropriate conclusion for those events and characters that continue on to an established work (the PJ movies), then what is the problem?