Less code runs as root than with X, since the server is far more lean.

There should be zero tearing or artifacts in Wayland, and the latency should be lower as well. Both due to passive compositing.

Screensavers are a pointless waste of energy. I'm not sure why you mention them.

In Wayland, WM/DE use IPC to communicate with each other; not X.

In theory you can run multiple XWayland servers to separate from each other. If security is a concern, Qubes might also be an option. And you're still more secure and better performance with Wayland plus some XWayland than with X.

I still don't see how it is more secure. If the WM can use IPC and tell wayland 'hey, I want to send this keystroke' or 'what were the keyboard inputs?' then why can't some malicious application do the same?

Can I run multiple wayland servers separate from each other? If not, then I still don't see how wm can prevent a random application from pretending to be a wm but actually being a keylogger.

The Wayland compositor does that kind of task, not the DE/WM like with X. That's why porting to Wayland isn't trivial. The server has many less lines of code leading to a lower attack surface, and lower latency or less tearing, and better HiDPI functionality.