Looking at material 3 widgets implementation, I think you missed one thing. For example, if you need your widget to have a specific style for a unique screen (all other instances of your widget have the default style), then you will have to style every child widgets. That's why flutter team designed their widgets with a 'style' attribute, in order to override the default one.

For sure, this problematic is important if you want to create a design system: how make your widgets flexible without modifying them.