Something about the old UI made it easier for me to understand that layers and pages were two sup panes. I think it was the fact that pages were indented a bit. It helped easily distinguish the pages and layers section of the left pane. Now with UI3 I find myself not being able to find where pages end and layers begin as easily. I need some sort of visual anchor here. My eye used to follow the negative space to the left of page names all the way down until I hit the layers area and now I feel like I’m going cross-eyed trying to find where my layers start and pages end.
I have the same problem. But how about splitting them into two different tabs? Resulting in 3 tabs for Pages, Layers, Assets.