There is really no excuse for a low-level API to be hard to use. It's just poor API design, plain and simple.
At the very least there should be a standardized (and centralized) client library on top of Wayland but below widget frameworks like GTK or Qt which implements the missing "desktop window system features": opening, moving, sizing windows (with decorations please), mouse and keyboard input events, clipboard, drag-and-drop. Non-GTK/Qt applications should never have to talk directly to the asynchronous Wayland APIs, only to this wrapper library.
Such a library should be designed to make programmers want to move on from X11 (because writing code against Xlib is horrible, but somehow Wayland managed to be even worse) - and tbh, this new window system client library (at first on top of X11) should have been the top priority of the Wayland project before starting to work on the actual X11 replacement, and it should have shipped on all desktop Linux distros at least a decade ago so that application programmers could have been won over (and for collecting feedback) even before Wayland shipped its first version.
I might be mistaken, but isn't this what libraries like winit exist for? It might not be just for wayland, but it seems like it supports everything you mentioned other than drag and drop.