>Want to list all the toplevel windows that are on a particular workspace so you can write a pager or taskbar widget?
I can do this with a trivial "jq" script in Sway with this command:
swaymsg -t get_tree
The problem is that the existing protocols are missing key functionality that desktop environment developers need (source: I am one).
Want to list all the toplevel windows that are on a particular workspace so you can write a pager or taskbar widget? Nope, can't do it. The foreign-toplevel protocol and ext-worspace protocol (the latter of which has been in standardization purgatory for 2-3 years now) don't know anything about each other, so you can't do that.
Want to write a widget that lists windows and lets you do a bunch of operations on them? Well, you can, if all you care about is minimize, maximize, fullscreen, and close. If you want to pin/unpin windows, move them between workspaces, resize them, or move them around on the current workspace... nope, can't do it.
That's just two examples off the top of my head. Looking at the list of Wayland protocols, and then digging in to figure out what they provide shows them to be immature and severely lacking.