NativeScript can do anything a native Java/ObjC app can do; you have full access to the actual native OS controls from inside JavaScript. And all controls that are created are actually the native controls; so if you create 20 Java/ObjC controls or 20 controls in NS, they are still all the exact same type of controls as far as the Android (or iOS) runtimes are concerned, all the screen rendering is done the exact same way since NativeScript creates Native controls.
Now as to complex UI's, I have several apps with fairly complex UI's, however one thing I do is I frequently start with a single UI screen and then once happy with it I take pieces that I can and have those pieces dynamically load in/out when they are needed to keep the UI as simple (light memory usage) as much as possible. The UI can handle complex screens, but by showing less items (and eliminating any hidden items from memory) the UI is way more responsive in any language.
