Generally speaking, DA:I .... demonstrated BW can't seem to get rid of the old good/bad divide - that we are the good guys that must save the world from certain doom and this is reinforced by the aesthetic of our enemies who are ugly, unreasonable and entirely alien to our understanding. This is a childish attempt in portraying conflict. BW should go that extra mile to make the entire notion of good or bad purely subjective to the different actors point of view. Both us and our adversaries should act for what is to be perceived our vital interests. We aren't trying to save the world/galaxy and our adversaries DON'T want to destroy everything. We have different points of view and interests therefore we end up in conflict. We will define them evil as much as they will do with us. The game should treat our adversaries fairly and make their motives logic and reasonable as much as ours albeit opposed and mutually exclusive.No one is good or bad in and both our (us and the enemies) motives are based on reasonable ideas. A conflict based on these premises will show that BW managed to evolve from the childish concept of absolute good vs absolute evil. Our world isn't made of absolutes but conflicting interests.
My take on what you are advocating for, to sum up, is a story/plot that involves self-interest versus self-interest, and these two are in conflict and both have relatively equal legitimacy - neither side is totally good or totally bad. And that this paradigm is more mature, whereas good vs. evil plots are childish. I do agree with you that propaganda perverts the facts, and can overly simplify the aggressive use of force as a G v. E paradigm. In real life that perversion of facts has caused horrific tragedies and loss of life.
I'm going to harp on your branding of BW and the G vs. E narrative as 'childish'. Per se, there is nothing 'childish' about the classic G vs. E conflict. Literature, both fiction and non-fiction, has wonderful examples of complex and mature narratives that involve G v. Evil. Protecting lives is not morally equivalent to those who seek to destroy lives. Good vs. evil situations really exist when the aggressive use of force against others involves the wanton and indiscriminate murder and killing of innocent people. Those are not 'childish' plots.
What can make them childish is the way it is written. The Grimm Brother's Fairy Tales are 'childish'; whereas the ME Trilogy stories are mature and adult food for thought (in the realm of sci-fi fantasy). Isaac Asimov's I, Robot is a mature investigation of humanity vs. their synthetic technology creations, most especially when the technology gives an A.I. the power to decide for it's own reasons that it will attack its creators. Where as a society are we going when our ability to create something, and such foolhardiness, is far beyond our so-called maturity to anticipate its resulting consequences? This is one of several classic and appropriately mature subjects to explore; it's not childish per se.
What makes a story childish, in my view, is the way the story is written, whether it is simplistic or cleverly complex, and the purpose or nature of the subject being written about. The Brothers Grimm wrote fanciful fairy tales directed at children, as are Aesop's Fables, but within them can be mature stories with a pointed lesson for grown-ups - if you are actually listening to what you are reading to your children.
I'm trying to think of good examples that would meet your criteria of a ' mature' plot (the opposite of childish as you see it) where both sides are neither totally good nor totally bad. At the moment, the stories that might fit your viewpoint is Conservative and Liberal advocacy, Domestic Car Companies vs. Imports, Tech Companies that are vying for market share, etc.
If you would post 5 or so story ideas that you are describing, I'll like to read it. Can you do this?