> Wayland is really slow.
I think you don't mean that the Wayland protocol forces slowness but that the compositor you used was slow. The one I use is fast.
> And if you don't like the window decorations (say, they take up too much screen space) your choices are suck it up, or if you're lucky and willing to spend a bunch of time reconfigure every different toolkit your apps use.
No, there are protocols to negotiate whether an app has server side decoration or not and the compositor has the last say.
> basic stuff that worked fine on X11 doesn't work on wayland in the name of "security"
On only the core Wayland protocols you're absolutely correct, you can't even implement desktop shells with those. This means there must be extensions and there are 3 different classes: KDE, GNOME, wlroots, with tools for and incompatibility between each. The wlroots extensions are designed to be accepted into the standard and for wider Wayland acceptance they probably should be.
Screen sharing is still a particular issue that we are starting to see solved with the advent of Pipewire.
Wayland desktops are definitely usable. I've been happy with a wlroots based one (Wayfire) for a few months and KDE before that (from what I see GNOME has been perfect for a while).
One of the last standing real issues I'm facing is kerfuffle with Nvidia drivers, especially the ones paired with Intel GPUs, but I think (surprisingly) Nvidia are actually working on fixing that.