> How do I use wlroots as a user

Why would you want to use it as a user? That makes zero sense.

> Is this why Xwayland exists, because it's so easy to do

I don't get your point. The reason it exists is backwards compatibility. There are binaries as well where changing a library is not so easy, and not every version change is equal within a toolkit.

But it's much different to go from X to Wayland then from Wayland to Wayland with one more protocol.