This claim, I'd like to point out, is a double-edged sword. The same way I may give them too much credit when it comes to DAI applied to the credit gives to the devs who created DAO.
Still, this is a matter that is irrelevant to my point - the fact remains that even you recognize that the way things are emphasize the themes that are there, fully and consciously explored in DAI.
Also - we actually HAVE NPC scenes/dialogues where Inquisitor either admits or can admit that they hardly recognize anyone. And not even random NPCs, but people who work for them. First is the Iron Bull's scene just after we reach Skyhold - they talk with soldiers, and not only Inquisitor admits that he didn't think who those soldiers are or what is their perspective, the fact that Inquisitor doesn't have an ability to know every person they work with or help was a point of the scene.
Another is Sutherland - you can totally have "uh, who are you?" reaction, and completely squander his potential by having Leliana send him to the kitchens or something.
I think Leliana mentions that the cliffs in Redcliffe are red because of the minerals in the earth there. And there has been no in game evidence that red lyrium alters the color of its environment, just a red glow of energy around things. And if the speculation supporting this environmental storytelling is correct, it will only be evident to us in hindsight, so I don't know that I consider that good storytelling. The storytelling should be evident at the time we play it, not after the next game in the series comes out and I go back and replay the game with new knowledge.
Totally untrue, especially in an ever expanding SERIES that entails more than games, none of which are self-contained. There were details both in DAO and DA2 that made only sense in context of what DAI has revealed.
Hindsight and recontextualization is a powerful storytelling tool too - how many people you think have replayed the game just to see Soals and what he said in new light, for example?
Or Flemeth, after the DAI reveal?
For environmental music or its lack, I really don't know what to think considering the issues with audio the rest of the game has. I don't see it as Bio deciding the EP should have no music to reflect the weak Veil. Heck, shouldn't all zones have no music then since each has multiple rifts?
Unlike other zones EP has been a regular battlefield long before the Breach appeared. Demons walk about the place with no restrictions (unlike demons from other zones) we can basically stumble upon them everywhere, not just around the rifts, and Solas basically tells us that the region has seen so much slaughter that demons will haunt it for ages to come. Whether the unpleasant "static" of a music signifies weakened Veil or just underlines just how utterly wasted that region is doesn't change the fact that it adds to the intentional unpleasantness of the zone. This is not a place made to look or feel pretty.
It's frustrating when the war table, where we're ostensibly sending multiple agents out for one purpose, come up with less herbs/metals/leathers than we do if we're strolling through a map for the same amount of time. And when we have to wait 16 hours for a mission only to get a sword pommel, it is anticlimactic. So when we are doing these small quests or picking up notes and following their directions, it makes me wonder why we're spending the time doing this when we could be giving it to the agents who apparently can't carry more than a handful of elfroot.
True, I'd like to see more mats being brought by agents, but I'd like to point out that Trespasser actually made many war table spoils more interesting. And ever since the beginning we could only get some unique schematics or equipment just via war table missions.
But I thought your point was that this environmental storytelling has replaced a lot of the dialogue and narrative storytelling of previous games. So if a lot of this environmental storytelling requires a lot of exploration off the beaten path, the overall storytelling becomes more difficult, or at least more time consuming, to consume.
It's arguable whether DAI actually replaced much. We'd have to get into details and differences between game and their structures, and I certainly have no head space for that now 
I could easily cut half of the zones and eliminate 75% of Skyhold's customization. Eliminate mounts, or reduce it to just horses.
You realize that Skyhold customization and reskins for mounts are an entirely different area of the game that has absolutely nothing to do with the narrative and was never even touched by the writers? You cannot seriously confuse art department's work to others', especially that most of the time you're not even talking about gameplay, or story... but reskins! That is nowhere near the cost of crafting narrative.
Besides, we heard from David Gaider that whether there would be less zones or not, it would have no impact on the length of the crit path.
Heck, remove half of the war table missions; it still takes resources to write them out, create a quest chain, design the rewards. Controversial, but I would be okay with human only and only one set of voices. I would also be happy removing all of these "ring quests" from every zone and only replacing them with a few better side quests. Even if the ratio was 10 ring quests to every larger quest, I would take that ratio.
Majority of those war table missions has been written while most of the work of the game has already been done. And it may take resources to write them out... but how many resources do you think it takes to write the dialogue (minding the word budget), hire at least 2 or 3 VOs to voices (and then translate them and hire VOs for German or French VO and all the work that comes with it), designing NPCs, animating possible cutscenes, finding or building new place in the zone, designing enemies and rewards and so on?
Like... I am not a game dev, nor I claim to know much about dev work, but it doesn't take an expert to see some problems here.
Also - there aren't even that many "ring quests" in DAI to begin with. There are 2 about rings specifically, but the entire amount of similar quests IS about 10. Really, at this point I have to ask whether you paid attention to any zone side-quest at all...