Unless you've got developer quotes that support your assertions about the Inquisition breaking free of the Chantry due to the Chantry being in disarray, you aren't being very convincing. I would agree that Cassandra is following Justinia's wish in creating the Inquisition, and that she takes the Inquisition off the ranch to prevent the disarray in the Chantry Leadership from focusing the Inquisition on the wrong goals, but none of that even remotely suggests that the Chantry itself is in any danger of losing their place in Thedas.
Mark Darrah and Mike Laidlaw have both said that the Inquisition is "in opposition to the Chantry", with Laidlaw adding that the Inquisitor isn't a "puppet of the church". David Gaider said that the Inquisitor doesn't work for the Chantry. Cameron Lee was the one who specified that Cassandra broke the Inquisition away from the Chantry after the cataclysm that kills the leadership of the Chantry and the mages (who attended the peace meeting).
Anora made an attempt that was convenient, and abandoned it when it stopped being so. That's not a quality you want to look for in an ally. And Alistair, regardless of what he thought he was doing, still failed. The Hinterlands are Redcliffe territory now, and "Arl Teagan" doesn't sound like a Dalish name to me. Even with the theoretical elven advisor, Alistair was powerless to circumvent the will of his people. Good intentions and a cup of coffee are worth exactly a cup of coffee when you don't follow through.
Queen Anora is also willing to give the Hinterlands to the Dalish in respect to the sacrifice made by the elven Hero of Ferelden who came from the Sabrae Clan, and that wasn't "convenient" for her; she has progressive ideas. Also, I'm talking about a treaty between Ferelden and an autonomous kingdom of the Dales, not about the developers (possibly) handwaving the Dalish Boon; I have a fairly good idea that more than a few Fereldens wouldn't want to see Orlais wield the same level of power that it once had. We also know that the army will follow the ruler's command, as the Crown can provide support to the dwarves in the Deep Roads who are trying to reclaim lost thaigs.
What, exactly, makes you believe that things would go any differently in elf/human relations if those 'knife-ears tried rising above their station' right there on the other side of the border? What makes you think the people of Ferelden would tolerate that any more than they did the elves setting up shop in Blightlands? Blightlands. The humans of Ferelden hate elves so much that even letting them settle on poisoned ground was unacceptable. And if the people of Ferelden did take issue with it, what is the monarchy going to do? Send the army after their own people on behalf of some 'knife ears'? Yeah, no.
If the Ferelden army is willing to tolerate going into the Deep Roads to fight darkspawn, I think they would be willing to tolerate fighting Orlesians.
An independent dales would be a rash on the Northern Ferelden border, and eventually it would get scratched. Probably with the help of the other human nation in the area, because when it comes to elves, humans are pretty much united on the proper course of action.
The Dales and Ferelden are actually separated by the Frostback Mountains, and (it seems) the land mass that would connect the two through the Frostback Mountains leads to the entrance to Orzammar.
All I'm suggesting is that if you think Ferelden is going to protect a nation of elves from Orlais, you are gravely mistaken.
I think a treaty would help matters, and I'm not as pessimistic about it as you are, especially as Orlais is dealing with a civil war and the crisis of the Breach (that may substantially weaken it in the same way that the civil war and the Blight weakened Ferelden). That said, I don't disagree that the Inquisitor might need to take further steps to nullify the threat that Orlais can pose to Ferelden and the Dales.