Visual UI builders for mobile cannot even handle reusable components directly. (Similar dialogs via mixin or inheritance, style extraction etc.) Custom widgets

Visual UI builders for mobile cannot even handle reusable components directly. (Similar dialogs via mixin or inheritance, style extraction etc.) Custom widgets? Amount of work to get them running in one of these is a nightmare. Compare that to game engines such as Unity or UDK and their editors, it's so bad it's laughable.