That Man is an idiot. Clearly everyone being dead is his preferred outcome.
Agreed. Teagan's character was assassinated in Trespasser. He should have known better.
No, he says the Inquisition's help was appreciated, but their goal was accomplished two years ago and they're still there. It's like Star Wars: everyone agreed to give Palpatine emergency powers, but he never relinquished them. The formation of yet another empire is probably one of Ferelden's biggest fears.
That's a separate argument though. Teagan's disagreement at that point in the game was that the presence was established at all. The Inquisitor even explains the reason for the presence (poorly).
And let's be honest, it's completely understandable that he's focusing on the Inquisition being around Redcliffe. That's his home/responsibility. The Inquisition either ignored a Tevinter force occupying his home to instead recruit the templars, or the Inquisition took the occupying force away without any real consequences happening to them (the mages), who then became somewhat heroes for helping close the Breach!
I disagree, but in any case, Teagan states none of these things. His problem is that you established the presence on Ferelden soil. He does not address that you've stayed there for two years, or who you decided to help.