What's complex for most users that do not spend their days into an IDE is not seing what's your prose is going to look like and they've been use to that for a couple decade. For us it kind of made sense to support markdown + giving giving a minimalistic toolbar for users who don't know how to md. Also, you can do a lot of things in BlockNotejs you can't unless you code html and css in md (colors, blocks etc.)

Well I think that most of our users have never typed a "[" character... So for them, Markdown is definitely complex :)