It is a matter of how we define complexity.

I think BUI stands out because of the intricate nesting and relational binding there is between elements and not only a lot of state, but precedents and context.

About intricacies, BUI can render css in its own engine, so if material UI widgets are necessary, it's just html layouts and css.

I think it accomplishes both kind of "intricate UI". I concede I haven't tried to see how material would render with it though, as it claims impressive performance, I doubt everything is GPU optimized, as even css itself doesn't have full coverage GPU optimisations in any of its browser implementations