Wayland by itself is simplier -- it is done by "outsourcing" everything a window system should do to the window manager.
There is where the complexity kicks in.
The resulting wayland environments are more complex because wayland itself refuses to define/include features that desktop systems are expected to have. This results in a sprawling mess of competing and incompatible interfaces for those gaps that other parts of the implementations (desktop environments) now have to compensate for by including multiple implementations of the same thing based on all these different interfaces.
