Well no, it's not necessarily that he hates the rich because he was born with nothing and is jealous (though I would say he'd be jealous of Bruce getting picked by Ra's), it's that he loathes this idea that they think money can buy them power, when in his experience money has nothing to do with true strength and power. He's a leader that gets his hands dirty and puts himself out there with his men. That earns him the kind of respect and loyalty that's priceless, the kind Daggett wouldn't know a thing about. Couple that with the fact that he was living down in a hole until Ra's schooled him in the ways of the world, and you've got a fully indoctrinated ticking time bomb waiting to go off.
In short, I think the sum total of everything we learn about the character, while much of it is left off screen and for us to infer and interpret ourselves, leaves you with the impression of a complex man with his own epic journey through life, just like Bruce.
Bane's statement to Dagget is a nice moment, but the idea of a man who thinks that brute force is power isn't all that complex. That's basically just describing a thug, a soldier, or a generic military leader.
This epic journey you speak of is largely unknown.
The nature of his indoctrination is largely unknown.
It'd be one thing if we SAW, or were even told that Bane had a journey similar to Bruce's, or saw or understood any of his indoctrination, but we didn't. Instead, we're teased and then told how he and Ra's ended up in the same organization, and that he loves Talia, and that he was kicked out. And that now he's Bane.
You're right...it's left to us to infer ourselves...because it's not at all present in the film. Any depth or story detail possible for the character is just completely glossed over in favor of building to a melodramatic twist.
Bane is more or less a fully formed but barely fleshed out, evil person.
He just IS evil and sadistic. Why? Who the hell knows?
He just IS a terrorist. Why? Who the hell knows?
He just IS devoted to Talia. Why? Because he was.
This is what I mean by thin.
So if Bane's primary weakness or thinness as a villain is that he is an extension of Ra's, so be it.
Bane's primary weakness and thinness as a character is that he's barely explored as a character.
He's largely reduced to his actions, the initially presented motivations behind his actions are both thinly handled and not apparently, by his own admission, an actual key motivation he has, and then there are a couple of expository passages about his past that turn out not really to be about him for the most part.
There was a fascinating character to be had here. They just didn't get to that point. We only saw glimpses of it. Which is a shame.