Maybe the author has overcome these issues, but I'd be inclined to go with a different editor. Also, ProseMirror's architecture is extremely close to DraftJS, which I've had much fewer issues with.
We then spent 2-3 weeks getting all of the formatting, tooltips and key mappings to handle some basic formatting (bold, italics, underline, bullet lists, numbers). Eventually, once there are more examples on the web of more complex formatting for the community I think it will become much easier to use.
It's the first editor I've used that felt like it made sense at a conceptual level but implementing "simple features" can feel very hard at times. I don't think that's a knock on the library though. There's a lot to learn and understand and it just took us a lot of time to get it all.
Just wanted to offer some feedback. Prosemirror's docs are woefully incomplete. The way controls are added is extremely confusing. Why do we need some node module called "prose-mirror-example-setup" ?
I know I'd personally prefer being able to add all the markup and style for the editor, and then just use prosemirror underneath the hood for state management.
Another thing that I found quite difficult, was programmatically inserting images at the cursor.
Finally, storing state as markdown has turned out to be a nightmare. Not really your fault, but perhaps something you should be aware of.
I also don't think the concept of fairness applies since I'm accounting the details of my personal experience and the conclusions I personally drew from it. Some of those are subjective (code quality) while others are purely objective (I got a lot of errors). What I infer from that may be entirely different from what you do, but that does not make your characterization of things more fair than mine.
The documentation is still no good. The underlying tech looks super promising, but the plugin system makes no sense.
If all they did was update their documentation so you can clearly see how to use it, perhaps it would be great.