I did a similar analysis a year ago and came to the conclusion that ProseMirror (https://prosemirror.net) was the right choice for my project. ProseMirror is an excellent toolkit for building your own rich text components and happens to also be written by the author of CodeMirror. It does not give you as quick an out of the box experience as slate (or any of the other rich text libraries out there) but its speed and flexibility is excellent.
