One of the oldest NativeScript performance tips has been to use a single GridLayout when possible, instead of nesting multiple FlexboxLayouts.
Minimising the depth of the DOM tree was the thing this advice was getting at. Cool to hear that it applies to the real thing as well!
If you render 1000 empty divs with absolute size and position and minimal CSS that'll also be fast! It's not the rendering that's slow, it's style and layout. Ignoring caching, style is O(num_nodes * num_style_rules), and flexbox/grid are O(2^depth_of_tree).