it has to do with how the walls are designed, the sight lines mostly force you to go straight in to finish it or you can't finish it with going around.
Take for example...
If you are on s2 on guardian, my sight lines are from camo, tree, blue room and I can easily make my way to you in many areas of the maps while being able to have an idea of where you ae.
Now, take for example those sight lines on plaza, it's so far away that no matter where I go you can easily get away bheehind a wall and lose the sight line and lose any chance of me coming after you. This is one of the main sight lines btw
Also, like you said rig, again, when i get out of the sight line, again its hard to finish you. Take for example the room next to snipe, I can see you across the sniper, but no matter where I go, I don't have a good place to keep shots on you.
But, again, take for example guardian, I am at top gold, I can push out to camo and still have shots on you, I can push out top mid and still have shots at you if you are s2.
I can make my way to top tree, or even blue room and still have focus to your position at s2. This makes a huge difference in the way sight lines work in halo 5. You can't push from different parts of the maps and have the same sight lines work.
Narrows- I can push bottom mid or top mid and still have shots on you at your flag spawn. I can go my OS and still have shots on you at the same position and vice versa. This creates wiggle room to go in different areas of maps and keep fire fights going. Halo 5 simply doesn't give this, it give you a sight line an that is just a very narrow tunnel of vision to finish a kill and good players wont die in those unless they are sniped. They can simply go hide behind a wall out of your siht line and you can't get multiple views on each other easily with moving around. i thoughtt the pictures showed this and if you played Halo 3 enough then you know what I am talking about without having to explain it I think.