Arkham Shadows had a good reason to end the way it did

Major spoilers ahead
Batman: Arkham Shadow
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Batman's Arkhamverse is filled with boss battles against the Dark Knight's main villains. Batman: Arkham AsylumThe mutated Titan minions and Bane himself would provide the basis for all the other brute enemies in the franchise; Batman: Arkham CityMr. Freeze will include all the dynamic and brain attacks players have; Batman: Arkham Origins would double CityRa's al Ghul's epic encounter for a cinematic test of parrying skills against Deathstroke; and Batman: Arkham Knight will finally allow players to get their hands on the Riddler after solving 243 riddles at the Pinkney Orphanage.

Batman: Arkham Shadow it's a much more linear and rigid experience than that Arkham games immediately turned into after Shelterbut it works extremely in his favor as Shadow takes a slower and more emotional approach to Arkhamverse storytelling. Batman: Arkham Shadow features three boss battles—two of which use new gadgets that players receive beforehand, and the other of which allows players to rely solely on their fists—and, unlike every other installment in the series, does not end with a boss battle. Instead of that Shadow achievement is the subtle culmination of the story he tells.

Batman: Arkham Shadow does not have a main antagonist in the traditional sense

If District Attorney Harvey Dent/Rat King/Two-Face were some sort of minor character, it might be easy to guess how a boss fight against that character might have ended. Of course, Two-Face later in the Arkhamverse has no problem with a coin deciding the fates of others and carrying dual pistols, and Batman has no qualms about brutally subduing him either.

however, Batman: Arkham Shadow chronicles a much more relatable and tragic portrayal of Harvey, showing him and Bruce Wayne growing up together and becoming family to each other. So for now Shadow almost had a boss fight for Harvey, as Camouflage's Ryan Payton told Game Rant, the idea was never as black-and-white as the boss fights experienced by players in the franchise: “We had talks and prototypes and games of various iterations None of them were the traditional 'Batman beating up Harvey Dent' – his adopted brother, someone he cares for and loves.' Peyton continued,

Obviously, we didn't put the boss fight with Harvey Dent at the end of the game for two reasons: one was really in terms of scale – we just put in as much time as we could with the amount of time and resources we had for this one project; and two, because when you zoom out of the story and see where Batman is as a character in the beginning
Batman: Arkham Shadow
and you see where it ends, I'm really, really proud of the fact that the players are up against the big bad guy at the end and Batman doesn't pull a punch.”

Batman: Arkham Shadow's Ending serves to develop the character of Bruce Wayne

Maybe it's the lack of boss fights Batman: Arkham ShadowThe final emotional resonance and seeing Harvey struggle with his disturbing prognosis as Two-Face is born hits harder than any punch Batman could have dealt him. For Bruce Wayne to not hug Harvey, much less Joe Chill, with anger or revenge is high praise for the protagonist and shows how much he's learned throughout the game. As Peyton states,

“He's sympathetic, and I think he shows that he's willing to understand someone who he may disagree with or who he's very angry with.

It's not just about Harvey Dent, it's about the man who killed his parents, Joe Chill, standing right in front of him, and I thought that was very important in how we conveyed that, so it had an edge over what I have some sort of traditional boss fight at the end of a video game.'