I rarely DNF and don't agree with the people whose automatic responses is that if you are not enjoying it, you should stop.

I think the more thoughtful response is to look at it through the frame of the author's intentions. Is this a deliberate choice on the part of the author? What is the intended effect? How much skill (or lack of skill) does the author have in achieving that effect, i.e. how good is the execution? If it fails, how exactly?

Personally, I don't think you can ever really know an author's intentions until you've finished the entire book. I try to withhold judgment until I can look back at the book as a whole to see what the author was doing. Then I draw my conclusions.

That said, it's a little different if this is not your first Brandon Sanderson book or even the first book in this particular series. By this point, you know who Sanderson is and what he's about.

I've read about 20 of his books, some of them multiple times, and I feel safe in saying that his dialogue is cringe because it lacks subtext. People say what they think and that's about it. Even when characters do have some more depth to them, he doesn't explore it in an interesting way because he simply tells us.

For me, it's not a deal-breaker. When I hit the cringe moments, I roll my eyes and move on. There's enough going on with the rest of the story to keep me reading. But I definitely understand why someone would think it's not worth it.