I disagree. Admins are complex. See https://marmelab.com/react-admin-demo/, it's a (fully working) admin built with material design and it uses about 30 specialized styled components. Think notifications, toolbars, menus, grids, etc.
Maybe it’s because I’m on mobile but that UI is awful. Things are oversized when there’s no reason for them to be. Lists can only show like 2 items on the screen without having to scroll. Useless.
The segments and categories sections have a more sane design for an Admin.