I've used prosemirror enough to have written custom nodes, commands, and custom code around its collaboration model. I got good results with all of this and I don't know any other platform that could have matched it.
The docs are thoughtful. There's an up-front learning curve to understand the architecture. When doing highly customized things, I referred to the source when needed.
For standard rich text, there are a lot of options. Prosemirror shines when you want to build on it as a platform.