This is an interesting contrast to Unity, which only has a very basic editor, but at the same time when I built a custom one, I only needed two classes for the whole thing. It was a lot of manual work (literally drawing stuff on a canvas), but it was conceptually simple.
Unreal is not conceptually simple, and I still need to manually piece together a custom node.
In practice, my past Unity projects usually had some kind of custom editor in them, while Unreal projects usually didn't.