How exactly is Hawke forced to choose? After everything that Hawke has defeated and how powerful that the game has demonstrated as being, what is forcing Hawke to choose? What's stopping him from legitimately either saying "both of you are crazy, I'm defending Kirkwall from both of you" or saying "I'm done and I'm out?"
This is still an rpg and a game and thus player agency should be respected.
Also, neither side is legitimate at this point. Meredith is literally overstepping her bounds by seizing direct secular power in Kirkwall and antagonizing mages based on paranoia. Furthermore, she had no legit reason to declare the Rite of Annulment since Anders was right there. But since she's crazy, she decides to attack the Circle whom she knows had nothing to do with the destruction of the Chantry. She was literally looking for an excuse and acted on one when it presented itself.
Then there's the mages. It's annoying and laughable that nearly every single mage in this city is either an abomination or a blood mage. Even the seemingly sane and respectable Orsino is a blood mage and had aided a known serial killer.
Why should the player be forced to pick a side that they have no reason to be invested in? That's literally a meaningless choice, especially when that choice leads to the same end regardless. There is no fun or engagement with a meaningless choice.
Mages: Fight templars; Orsino goes crazy and dies; Meredith goes crazy and dies; Hawke disappears; and Mage-Templar War begins.
Templars: Fight mages; Orsino goes crazy and dies; Meredith goes crazy and dies; Hawke disappears; and Mage-Templar War begins.
If the outcome makes the choice meaningless anyway, then you'd might as well let the player come to that end on their own terms. That makes the situation more immersive because you are able to act as your character sees fit.
The situation would be much stronger if Hawke tries to save Kirkwall from these two mad houses, but the rest of Thedas still erupts into war. It would also be an interesting deconstructive angle to have the so-called hero abandon the city that they're supposed to be saving because the hero didn't believe that there was anything worth saving.
Because Hawke was never a world leader in the first place. Hawke is a refugee who struggled to make a home in Lothering and build a circle of friends. As Hawke, I don't want to completely revamp the world. I'm just trying to survive. You fight big bosses... to survive. You go to the Deep Roads... to score coin. You don't go to the Deep Roads to revolutionize dwarven politics. You don't come to Kirkwall to change the structure of the chantry. You are really just a participant. Anders is the revolutionary, you are not. And by the end of the game, I felt like I was Hawke and I understood - yes, I'm forced to choose a side because I'm not going to be stopping both sides. I'm going to be caught in the middle and the sides are going to play out no matter what. Just because you dueled the Arishok doesn't change the fact that the Arishok was a rogue Qunari and the Qunari state didn't sanction his actions anyways - you were just a champion. A celebrity, really, not a viscount or politician. And when you defeated the Arishok, it made a statement like "yes the people of Kirkwall can fight back" and you became a symbol of the people, but really you're just one of the people.
That's another thing that worked too - your companions were honestly more impressive than you were. Aveline was a Guard-Captain, and yes you were a critical friend whose support ensured her station didn't get swallowed up by the templars, but that's what you were. A supportive friend. She was the Guard-Captain maintaining order and have a true station in that city. Anders was a leader of an underground mage rebellion and he was the one blowing up the chantry and you couldn't do anything about that.
And I did feel player agency. I felt player agency because I could either be remembered in retrospect as someone who stood with the mages ,or someone stood with the templars, I could slay Anders or not (especially if romanced this was potent), my brother or sister could be a grey warden or dead or templar, etc, Merrill's entire clan could be slain, Merrill could see the error of her ways, or not, Aveline's life could be shaped by me, or not, Fenris could be sold back to slavery or not, honestly... all these influences were on the companion-level and I guess that's what the game was. It was a smaller sphere of influence about a refugee making a name for herself, it wasn't a godlike hero reshaping the world around her. Some people probably subjectively don't like that, but I did. I made choices I could within my sphere carved into a pre-existing world.
And I have EVERY reason to be invested in the choice. That's the thing about DA2 - I'm more invested in the choice than in any other game. Because I'm stuck in that world and for ten goddam years have seen my mother killed by a blood mage, templars going too far, my lover driven insane by mage-templar politics or magic in general, my brother or sister being consumed by either faction, my bestest friends each impacted in very serious ways by the various dynamics.
Meredith isn't legitimate and IS going against policy, but what can you do about that? You're in the city and she's making the decision right there and then, the grand-cleric is gone, and you're surrounded by Meredith's templar forces. It's not like you can escape and go to Val Royeaux and gather an army - that's not really your personality or goal, there is no time, and honestly you're just a citizen of Kirkwall in the middle of trying to defend yourself and your home. If you don't choose a side you'll be slaughtered in the middle, that's all it is. Like Anders said, there can be no compromise. And then Merrill is like "nooo" and then you say "the choice was taken from us. Anders took away the choice." So there's that too.