Guinan's ability to see through different timelines has never been properly explained in the same way we never knew why Q was wary of her. I've read some silly explanations like, being a race of listeners, they would never fall for the Q's tricks, which is very absurd because we know some can be corrupted. Personally, I think it's one of those things that the writers didn't really want to spend more time with and simply said "she's mysterious" and be done with it. I mean, in the same universe, Wesley was just born a genius without more explanation than being born this way by chance. So, Guinan's race just
know things. The part of the Nexus is just something they added up later to make her a guide for Picard for his time inside the Nexus and it makes sense her mysterious character does this.
I've seen some clips of this show and you are sadly right. The writers just want to take the characters from point A to point B without any further explorations of their ways. It's just "thing happens" -> "let's solve thing" -> "move on to the next thing." All while trying to sound smart and inhumanly assertive.
Remember how the whole crew was debating whether it was proper or ethical to help that kid from "Pen Pals" and her people because not helping meant they just would ignore the death of millions of living beings despite they could so something?
https://youtube.com/watch?v=4mH-L6UCCAE
Moments like these were the core of ST:TNG. No yelling, not trying to outsmart the other, offering different points of views to reach to the best solution, all while showing each character's personality: Worf is a pragmatic absolutist, Dianna is indeed empathetic, and Data offers the human point of view while Pulansky, formerly sceptic of him, takes his side.