I think what you're sensing is a desire to ramp up the conflict. Especially for a longer series, you need the stakes to increase with each book. First there's the enemy, then friends start turning against each other, and soon there's no one left the protagonist can trust. It's dramatic.
But there's a problem. This can fundamentally change the tone of the story. How many times have you heard someone say a movie started out great but then got weird/dumb/boring? Oftentimes this is a tonal shift that they didn't enjoy.
Authors writing books can fall into the trap of building a wonderful, pleasant world and then suddenly realizing they need to "get serious." It's hard to hold on to your original tone while upping the ante.
So how do you accomplish this?
1: Make it personal
We think that making the conflict bigger means adding more that could go wrong. Instead of a town, endanger a city. Instead of an empire collapsing, just threaten the whole world. But the problem is that people cannot empathize with the world at large. It's too general and too vague. Instead, the way to really hook people into the conflict is to make it more personal. What does the protagonist stand to lose? Increase that, and you've increased the stakes. This might mean simplifying and focusing your story. You don't have to snuff out all light everywhere; just give your main character a harder struggle, and let that complicate the possibility of victory.
2: Prepare the reader
The other thing you should do is prepare readers by subtly warning them what's to come. Don't surprise them too much with the nature of the opposition. If your protagonist has a weakness in chapter 1, that should be the exact pain point where the antagonist presses. This way, people are prepared when the conflict deep-dives. It won't be a frustrating, unexpected turn. Plus, we've already seen that the character is weak there. It's the best possible place to find conflict.
EDIT: I thought more about this and came up with a third point. It might be the most important.
3: Have an anchor
I can't tell you how many TV shows I've started, only to drop out when the last character I cared about was gone. But you know what? It's not usually a case of them dying. What happens is that they buckle; they lose track of what they've stood for, and I no longer respect them.
Fair warning: I'm an optimist with low tolerance for gritty stories. I don't read much dystopian because it's too bleak for me. BUT I can withstand an awful lot of darkness if there's at least 1 character I can always root for. I can't emphasize enough how important this is. What I need is someone with moral fiber who won't give in no matter the pressure. Some might call this unrealistic since there are no perfect people in real life, but stories have always been abstractions. We need someone representing what is good.
For me, as a reader and viewer, having that anchor character is vital. And you must preserve them. Put them through trials and tests, yes. Give them doubts, absolutely. But don't let them cave, or you've lost the last string of hope. Because the anchor represents not just their own personal goodness but the whole concept of what is right and true.
If it's helpful, here are 2 examples.
- I loved the first season of Downton Abbey, but I quit when I lost my anchor character Robert Crawley/Lord Grantham/the dad. In the midst of relational drama, he was the one character who was both significant to the story and untainted by his choices. But then he cheated on his wife by kissing another woman (even as simple as that action is), and I no longer had anyone I truly believed in.
- On the flipside, Samwise Gamgee is a wonderful example of the good character. The Lord of the Rings is a dark story, but even in the far reaches of Mordor, Sam is still believing that they might succeed. His faithfulness is where our hope rests.