The lie that preserved Dent's innocence corrupted all the good that Gordon did in Dent's name and the lie that Alfred told about Rachel ended up destroying his friendship with Bruce.
Which was kinda the point.
One of the reasons why
The Dark Knight is so great is because it is, above all, a character piece. Even with all of Nolan's intricate plotting, what the film is really about is showing all the different sides to each and every character. The Joker is trying to prove that everyone has a dark side. That everyone can be corrupted. Even someone as supposedly good as Harvey Dent can fall from grace. The Joker questions Batman's methods, and at many times during the film Bruce himself even questions if he's doing the right thing, is he going too far, etc.
There's a point in the story where Batman uses the sonar device to tap into people's cell phones so he can triangulate The Joker's location. Lucius Fox says that it is going too far and that so long as the machine stays at Wayne Enterprises, Fox won't. There's a lot of moral ambiguity to
The Dark Knight which makes it so fascinating. Even the heroes are incredibly flawed and go to some pretty dangerous and morally questionable lengths to accomplish their goals.
Batman thought that by preserving the lie he could stretch Dent's good image for as long as he could. Even as
The Dark Knight Rises begins, that plan kinda worked: Gotham believes Dent was the White Knight he advertised himself as, and Gotham bought it. Then, when Bane comes into the picture, he completely shatters that. Gotham sees Dent for who he was, and whatever Batman and Gordon did to preserve Dent's image and "save" Gotham failed. When Gordon is injured and lying in the hospital bed, he says that Batman must come back, but Batman says that "they won". Batman believed they had won, that Batman is no longer needed, that Dent was the true savior of Gotham, but once that is shattered, Batman is needed again. Until John Blake enters the picture and Batman realizes there is someone to give the mantle to. Someone worthy of taking up the mantle of The Dark Knight.
The Dark Knight was all about characters, even the heroes, making complicated and difficult decisions in order to do what they see as "right".
The Dark Knight Rises is all about the consequences of those decisions and the impact they have.
Blake was right and Batman was sacificed to keep a lie going. And while Bruce Wayne might've retired in hte Nolan trilogy he's making his way back in Superman Vs Batman.
Nolan's movies are separate from this new shared universe, though. Ben Affleck isn't the Christian Bale Batman from the Nolan universe.
In the end Batman in The Dark Knight has been declawed, he can't kill and the criminals know it and the lie that makes him a killer takes away any good he's done. So in the end Bruce has lost Rachel to Harvey and he's not even premitted to know that either. I can't see how that's development at least not a good development of character.
If anything, Batman at the end of
The Dark Knight is the vigilante that he pretty much is in the comics. Not working with the law, and seen as a dangerous figure to the criminal underworld. In the comics, Batman strives on being an urban legend and spreads that image as much as possible. People think this Batman figure is a lot worse than he actually is, and at many times in the comics Batman uses that to his advantage.
The purpose of the lie, though, was very much setting up the conflict that Batman would eventually get absolved. As
The Dark Knight Rises begins, Gordon says "It'll be a very long time before someone inspires us the way Dent did", or something along those lines. Dent was a temporary figurehead. He was never meant to be Gotham's white knight or savior. What Nolan was doing was setting up for Batman to be redeemed, his image restored and for Batman to be the savior that inspires Gotham to do good. Even more, Bruce doesn't have to be that symbol anymore and can move on with his life.
Like I said before,
The Dark Knight is all about characters making difficult decisions, and sometimes those decisions aren't the right ones. Batman thought that by taking the rap for Dent's murders, he was doing the right thing by creating that lie. In
Rises, he learns that was a mistake and he faces the consequences of that mistake. If that's not character development, then I don't know what is.
So is this some kind of reboot for Batman and we're looking at new Batman or a contuation of the Nolan trilogy?
This Batman is a completely different character. It's a reboot. That's one of the reasons why Christopher Nolan, who was an executive producer on
Man of Steel, is not involved in the
Batman/Superman film anymore.