Wayland has a bright future ahead: The move from Xorg to Wayland had a rough start, but things have improved, and there is an exciting roadmap for the future.
I never heard of AltGr reffered to as "Meta", except maybe in the sense of "Emacs modifier" which might be bound to it. Super is definitely the key between LCTL and LALT though
There is actually less to ’xkill’. It nukes the X window from orbit in a very violent manner. The owning process(-tree) will usually just instantly curl up and die.
The main benefit is that it doesn’t actually kill the process, it only nukes the window. As such, you can get rid of windows belonging to otherwise unkillable processes (zombies, etc).
Also, it’s fun. Just don’t miss the window and accidentally kill your WM. (Beat that Wayland)