Has continuously added every little UI component imaginable therefore is rarely used as per exact needs of the user or in the right context of the interface. Being the fragmented OS in it itself, does not help the overall experience.
Best example of convolution: FAB vs. Menus // Navigation drawer vs. "Bottom navigation" (Tab bar)
Has a somewhat restricted and lean set of UI components within the guidelines but not a single extra component was added since its launch therefore is somewhat lacking proper usability from the base OS level. Given that there are now various device sizes, original component set simply cannot cater for the best experience.
Best example of UI deficiency: Most primary actions are still at the navigation level, top of the screen
Perhaps it's time for a UI refresh?