Well, I opened this topic when it was looking like enabling the WYSIWYG editor would make the markdown one monospace (cf Monospace font in the Markdown-only editor - #58 by mbauman ). I’m very glad that’s no longer the case and that this is now configurable, because, yeah, I’ve never met a markdown WYSIWYG editor I liked. This is getting close, though. 
I write a lot of markdown in a lot of text-boxes (in both rendered and non-rendered contexts… to the point that I almost consider un-rendered markdown “formatted”), and I know I’m quite the outlier. I do think, though, that there’s a cluster of us outliers, and we tend to gather in the context of programming language forums.
The most valuable part is to make the auto-formatting as predictable as possible, so I can learn when I need to backspace, but that’s quite hard to learn in my experience.