The Problem with Trespasser
So there has been said a lot about the flaws of tresspasser as a finale to Inquisition, as it can basically be divided into two sections.
There is the lore, the character stuff with your companions, and the actual titular trespasser section of the story, which is generally liked.
Then there is the Exalted Council part of the Story which is generally greatly disliked for the way it portrays Arl Teagen as an ungrateful arse, who even though he's in the right that the Inquisition really does need to disband, is such a bitch about it that a player might feel the desire to keeping it intact just to spite him, despite all the reasons that is a terrible idea(Such an organization being doomed to become the templars 2.0 being the single biggest). Not to mention the way it makes Thedas's nations look like they have the memory capacity of a goldfish, given how instrumental the inquisition was in stopping the last massive threat and might be so again against the plenty of obvious threats on the horizon(and sure enough, the stop the Dragon breath terrorist attacks that would have happened with or without them being there).
However, looking at the big picture, i don't think the actual writing of Arl teagen was the problem here.
No the problem is that Arl Teagen and the rest of the world's reaction to the Inquistion is very, very clearly taken from an older draft of this story, where the Inquisitor was far less... An unambiguous force for good, lets say.
The concept art for inquistion tells a story that is very, very different than what we get in game, with a lot more emphasis is put on the inquisitor very obviously being a dick, that is not well liked by anyone around them.
There is also the way said inquisitor could be far, far more pragmatic and morally grey or dark, like here, where the Inquisitor could force the Venatori to serve after defeating them.
Way more emphasis is built on the idea that the Inquisitor is creating a cult of personality around you, personally.
Essentially a dark mirror to the Hero of Ferelden and Galahad's journeys to defeat their own crisis'.
The option of letting celine die was always gonna be a part of the game, but rather than a pragmatic, move of standing aside and let it happen, your companions would have very negative reactions to this choice, with you having to force Blackwall in particular to stand back as he curses you.
And of course, it would all cuminate in the logical endpoint for the herald of andraste, the living embodiment of the Andrastian reformation as you took your place on the sunburst throne, and usher in whatever changes you want.
This outcome... makes perfect sense. Frankly speaking, this is a much more narratively fitting ending for the inquistior, that has a clear climax from where they start.
Of course we all know this didn't actually end up happening. The Inquisitor ended up being the most passive of all the PC's by a wide margin(you could shape them into having a personality, but not one with a true backbone like Hawke and the Warden), and all these very morally dubious options was taken out of the game in favor of a much more morally simple story.
The most evil thing you can do in DAI is to choose the templars over the mages... and rather than being portrayed as the clear evil choice as it should have been(and still been a legitimate and pragmatic option for you to take) there is instead attempts at making it more nuanced.
Other than that, you don't have the kind of options that the Warden had, and even hawke did(like selling Fenris into slavery), to be a dick.
With all this in mind, it's blatently obvious why Teagen and the world is so damn afraid of the Inquisition.
Because this part of the story was written from before this change in the direction of the game, and was never updated to fit the final product.
If the original vision of the game had to to pass, Teagen's extreme reactions to the Inquistion would have been far, far more understandable, and in it's own way a way of calling the player out on their bullshit.
However, the final product just makes it appear he's way overreacting, rather than maybe questioning that maybe Teagen is right, maybe it is time to end this inquisition for the good of all.
Its one of the biggest problem with what is otherwise a very good epilogue to Dragon Age Inquisition.